well, there are some usable compressors that you might find; mixing and matching will be important in the case of cheap stuff, however. If you've got 8 channels of cheapo compressors on everything, it's gonna build up a sonic 'signature' that'll sound...well...cheap.
The Behringer Composer Pro is a fair bang for the buck comp; I HAVE seen them used in studios that have much more expensive options. One of those for a $100 gives you 2 channels. (or stereo). Send in that warranty card!
DBX 266xl gives you two more that'll sound a little different (that's 4 for $200).
You could find a Symetrix unit (525 or the like) on ebay for about $100. They're pretty cool-I've got an old mono 501 that I like on bass. (that's 6 for $300).
You could pick up an Ashly stereo comp for around $100; lots of folks like 'em, but if I were you I'd buy an RNC (mono/stereo comp) for $175. It's actually a good, versatile comp that you can use on about anything. (budget: $475, 7 channels, but the RNC can be used stereo, just not dual mono.)
Chris.