If you take a look at some of the contester-websites, you'll see huge towers with stack of yagis pointing in every direction. But as few of us have the land or the cash, we need to think of other ways to go. First of all, you need to define your objectives, in terms of which bands you want to operate from, and which areas of the world you need to cover. It is nice to have a big signal on all bands 160m-10m, but if resources are limited, you could take the bands one at a time, and spend a year operating all the contests as a single band entry, and then the following year choose another band. This way you could have a great monoband antenna where a multiband setup isn't practical, as well as needing only one feedline and support.
To rotate or not to rotate ?
The big contesters know how much time can be wasted waiting for the beam to swing around, so they generally have fixed antennas on all of the main ham areas, and use the rotating beam for multiplier catching. If they can cover the areas where most of there signals will come from, and be able to switch between them quickly, they are happy. From the budget contester's point of view, this idea is something to stick with too. Have you seen the price of rotators lately ? The ones that can handle those big beams are pretty pricey, so doing without is worthwhile. A lot of contests are based on specific areas of the world, so if you've got your antenna pointing that way, and its beam-width is not too narrow, you'll be as good as the next guy and won't waste beam-turning time either.
What antenna-type to choose ?
This depends a lot on your situation, but there are a few ideas that may be useful. The big contesters stick to yagis because they can buy them off the shelf, you can fit plenty on a tower, they don't need adjusting during the contest, and their gain, front-to-back ratio and beamwidth all make them a great antenna to use. The downsides are the big support towers needed, the rotators, and of course the price. Just check out the price of a monobander or a non-trapped multibander and you'll see what I mean. Homebrew monoband yagis are a good possibility if you can afford the aluminium tubing, but for best value its best to stick to wire which is cheap and easily obtainable.
Single or multiband ?
When home brewing antennas, a monobander is generally easier to construct and get working properly. Don't fall into the common trap of using traps ! They are poor performers in anyone's book, reducing gain and bandwidth; they are best forgotten about. Better to use multi-dipoles attached to the same feedline and supports, either in a fan or using multi-core cable. Better still, a big dipole fed with ladder-line that can be used on many different bands - more on this later.

The idea of obtaining a multiband antenna by putting seperate monoband elements on the same support structure is valid for other designs too. The most obvious is the quad, with its seperate elements on the same spiders, but yagi manufacturers also go this route as well. Both of these work better with separate feeds for each band, or a relay box to choose the one you want, though there is one antenna, the log periodic that keeps everything on the one feed line.
Rotatable options.
If you are determined to go for a rotatable antenna, then the best value has got to be the quad. This antenna is formed from one or more full wave loops per band, and makes a great contest antenna. Its good points are that its a loop so its low noise, there's worthwhile gain and F/B available, and they are not too difficult to make yourself, especially if you don't try and pack too many bands on the one framework. We even have a quad expert here in Ireland - EI7BA down in Cork, so check out his excellent website and see what he has to say. Other rotatable wire antennas include the ARRL's Telerana, which is a log-periodic and hence multiband; and the VK2ABQ tribander which is useful for those with a limited space.
Where's North ?
Once you have your antenna up, its important to make sure its looking in the correct direction. To work that out, you'll need a Great Circle Map centered on your location. You can pick one up in my Download section, or check out the Links Pages for software to make your own.

You'll also need to know where true North is. People can get mixed up when it comes to finding out the correct magnetic deivation for your area, then applying it correctly, so a simple solution is provided by Pete, N4ZR, who says 'Get your local paper and find out when local sunrise and sunset are. Split the difference. When that time arrives, go down to the tower and see which way its shadow points. That's true North.' Simple when you know how ! Alternatively, if you are determined to be more technical, follow Dave, AA6YQ's advice - he says 'If you know your QTH's latitude and longitude or grid square and your PC's time is accurate (using a freeware internet-accessible atomic clock like AboutTime, DXView will tell you when the sun is exactly true north of your tower - see www.qsl.net/dxview. If your rotator has a PC interface, DXView will control it for your, displaying your beam heading and the solar terminator on a world map. And its free.'
Fixed Wire Beams.
Some very useful fixed wire antennas with plenty of gain can be made for small amounts of money. Most of the handbooks have designs in them, so you don't have far to look. A vee-beam is very simple and effective, and could be mounted on a single support with the arms sloping down to near ground level. Its bigger brother the rhombic is used by some, and there are websites where you can find out more information - see my Links page. However, they may not be the choice for everyone; here's what K6HI says on the subject:

>Rhombics are a good choice when wide bandwidth antennas
>are required and unlimited land is available. 

>Factually, Rhombics have the lowest gain for pattern beam-
>width of almost any directional array. They have the lowest
>gain per acre of space.

>The radiating efficiency of a normally terminated Rhombic
>(with a resistor rather than a recirculating device) is
>always less than 50%, and they gain limit (over earth) at
>about 3.3 to 4 WL per leg because it is impossible to force
>enough current into the outer portions away from the feedpoint,
>and because of all the minor lobes.

>On the plus side they have very wide bandwidth ( when terminated)
>and are simple designs. When a station has a small budget, a 
>large land area, cares less about side lobes, lots of power, and
>operates over a wide frequency range Rhombics are a good choice.
>But not for gain per acre or gain per beamwidth.

Wire yagis are a possibility though information is sparce; Les Moxon suggests that good value can be obtained using long, wire-yagis made in inverted-vee form and requiring only two supports. Likewise, the wire log periodic is cheap and easy; some have made inverted-vee versions or even vertical log-periodic beams that would require just a single support. W4AEO wrote a great series of articles on wire LPs for HamRadio magazine in 1973.
Beverages.
How about a very simple wire antenna used by a lot of the top contesters ? We're talking Beverages here, and apart from the matching transformer, they are about as simple a receive-only antenna as you can get. They are cheap to construct, and as long as you have the space, an unbeatable option for the LF bands. You might think you need miles of open grassland for good results, but many use them through woods etc with great results, and if you've a wood next to you, thats the supports taken care of too - just buy a bag of electric-fence insulators from your local farm-supply store. If you live in the city, buy a drum of black wire and run it along the tops of fences etc. when the neighbours aren't looking - a 'stealth-beverage.' For many, the beverage is a seasonal antenna, making its appearance for the autumn contest season and disappearing in the spring. W2UP suggests a simple support system, consisting of 3ft lengths of rebar hammered into the ground. A length of 1.5" PVC pipe is slipped over the rebar. At the end of the season, the rebar is pulled out of the ground and saved for next year.
Receive Loops.
Not got the room for a beverage ? How about a receive-only loop for the LF bands. This can easily be made at home using bamboos to provide a 6-8' diameter support. Because its a closed circuit, its a lot less susceptible to noise than long wire or vertical, and its rotatable too, which can be very useful for nulling out the interference and improving the S/N ratio. You will find a site with homebrew loop information on my Antenna Links page, or just have a look in one of the handbooks.
Sources for wire.
The dealers would have us buy that nice drum of hard-drawn copper for all our antenna projects, but a variety of other wire can be used as long as it suitable for the intended job. A 160m dipole made from standed wire would soon stretch, and snap in a wind, but used for HF antennas it might be OK, and for buried radials, just the job. Secondhand wire can often be found at scrap dealers and bought for little more than the cost of the copper content. Utility and telephone company often replace cables which would make ideal antenna wire. Sometimes, the multicore cable has additional steel cores, which are great at stopping antennas stretching over time. Sometimes its not in the right lengths, but there's no law that says an antenna has to be made out of one piece of wire. Knot it well, solder the ends together and make good the insulation with a piece of tape.
Still on the subject of wire - Have you seen the price of rotator-control cable ? There's no need to buy this stuff, as any multicore cable will do as long as it has sufficient current-carrying capacity. For long runs, house wiring cable can often be cheaper. The same applies to preamp power cables, and other control cables for remote switching etc.
Verticals.
One antenna-type not to forget is the vertical. For LF contesting, paticularly on 160m, a top-loaded vertical is the antenna of choice, but even on the higher bands, a vertical with its low angle of radiation can still be useful budget antenna. We are not talking anything fancy here - a vertical is a piece of conducting material suspended vertically. It can be self supporting aluminium tubing, old copper pipes or electrical conduit; and who can forget the Bean-Can vertical, which as its name suggests was made by soldering together sufficient baked-bean tins to get the correct length.

Any vertical needs to be insulated from its mounting points, which on a vertical supported at the base can be done by surrounding the section thats clamped with an old piece of polythene water pipe, or if we are talking about a guyed free-standing vertical, just sit the bottom end in an old coke bottle. If the upper portions are guyed with plastic rope or bailer-twine, you won't need insulators there. Verticals can also be made of wire, supported by a tree, or from the guywire of a tower. Some have even used kites and balloons to support a big LF vertical although the Aviation Authorities generally impose an upper limit on this.

You could make a vertical array by phasing two or more for some directional gain, and the 4-square array, which as its name suggests is an electrically steerable array of four fixed verticals, is used by even the biggest of contest stations. For the budget contester, its important to remember that dollar for dollar, a phased vertical array is a much better bet than a big LF beam at a sensible height and suitable tower or rotator. Spending a few dollars on wire for the radials doesn't seem so bad any more, does it ! The more radials, the better.
Feedlines.
The feedline of choice these days is of course coaxial cable, or 'coax'. There are many different types available, but buying cheap coax is not a good idea due to the losses involved. A budget contester should not cut corners here, but stick to at least RG-8U of good quality. Hardline is even better - just check out the loss-tables in most amateur radio handbooks and find out where those DX signals are disappearing. There's no point losing those hard-earned dBs from amplifier or antenna down a cheap bit of RG-58. Here's something to ponder on - for the budget contester wishing to improve his station, the 'dBs per dollar' figure for good coax is a lot better value than a new linear amp or yagi. Be careful also about second-hand coax. It could be a good deal, but could also be a complete waste of time if worn, damaged or corroded. Check it out first, or you'll be wasting your money.
Reduce your Feedlines.
With the price of good quality coax being what it is, an option for those with antennas grouped together is a remote coax switch, which can be purchased or home-made. The control cable will be a lot cheaper than multiple coax runs, and as long as the switch is well constructed, will have a minimum insertion loss, especially at the lower frequencies used by HF contesters. Whilst on this subject, Dick, WC1M suggests a home-made remote switch box for your antenna rotators as well. Not only are you saving on cable, but you only need to purchase one controller. I use this idea, though switched at the shack, and the switching is easy enough to do, though I would recommend powering down the controller when switching between rotators.
Open Lines.
Before the days of coax, everyone used open-wire lines to feed their antennas. Its disadvantages are that is not always easy to get in and out of the shack, it must be suported away from the ground and metalic objects, its hard to use on a rotating beam, and it requires a tuner at the transmitter end. However, don't give up just yet ! It has a lot of advantages too, such as low loss over long runs or high frequencies; it handles high power well; but best of all for the budget contester, its very cheap.

The construction requirements are two wires separated by insulating spacers. The wire doesn't have to be anything special, and its not under any tension either. The insulators can be home made from any number of materials. A few ideas I've come across are wooden dowells boiled in wax, old ball-point pens, strips of plexiglass/perspex, of lengths of electrical oval conduit. There's nothing magic here, and it works great. Consult some of the older handbooks for ideas about using and routing it, and aim to keep it about 10" away from anything else.

For the budget contester who lacks the cash or real-estate to go for resonant antennas on each band, a doublet, as big and as high as you can get it, fed with ladder line is a great multi-band proposition. The tuners are easy to make, and if you are worried about speedy band tuning, try K1ZX's idea of cutting out a piece of card so that it slides over the shafts of the variables, and hold it in position with a piece of tape. You can then mark the card with the correct adjustment positions for each band. He suggests a different colour pen for each band to save confusion. This idea works great for linears and valve transmitters as well, when you don't want to permanently mark the front panel.

Normal People.
So, you've got this far, but are still not convinced you can do without that stack of monobanders ? Well, the following might be of interest you, extracted from a survey in the RSGB's 'Radio Communications June 1992' magazine, based on a poll of all UK stations on the DXCC Honour Roll at that time....

Some had very small lots : one had a garden only 16ft square behind his house.

Approx 50% used three element tribanders. Those who had moved to quads reported they were not going back. All quads except one were two elements - the exception was the famous G3FXB quad, which had three elements on 20, four on 15, 10.

Antenna height: Only 3% used antennas higher than 60ft. 40% used 60ft, 30% 40ft, and 14% 30ft.

Only three used directional antennas on 7 or 3.5Mhz. Only one had a rotary on 7MHz, none on 3.5.

Good results were reported with very modest whips etc. on 7MHz. The consensus was that one could do well on 3.5 and 7MHz with simple antennas, but that it was necessary to experiment with whatever will fit on the site until it is discovered what works for you.

So, quite a lot can be done with modest antennas. Don't forget, these weren't occasional operators, they were operators on the DXCC Honour Roll ! Food for thought, I think.