They are pretty easy to build. The surplus sites usually have IR LEDs fairly cheap. I used perfboard, saves drilling a lot of holes... From a 12volt supply, you can run 9 leds in series, with a 47 ohm resistor(might want to recheck, been a couple of years), and you can put as many of these as your power supply can provide current for. Mine do pretty good with 54 LEDs. Wouldn't get too crazy though, if the camera is B/W, and sensitive, you will flood the scene, and you will only see white. Most color only cameras have a filter, and might not pick up much at night. Learned the hard way, now most of my newer cameras are day/night and have LEDs built in, don't really need separate illumination, but use them anyway, since I built them...
If you are really low on funds, collect a bunch of remotes, usually good for one or two LEDs, and who doesn't have a few useless remotes laying around, thrift shops will probably have a few cheap as well.
SALE! Powerful IR LEDs-The Electronic Goldmine
These are mixed, but 20 for $1.49, compaired to 20-30 cents each...
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Little pricey, compared to just building your own from scratch, but might be in your range.