Precicely what Eeldip says.
The compressor to look out for is
the Symetrix 501. Before the RNP came out, it was the favorite budget compressor used by a lot of pretty big names, actually as a bass guitar comp. Still used a lot for that purpose today, actually.
Here's a tip for you, by the way: Be on the lookout for
the ones with the toggle switch. The toggle switch is one of the first models they made, and it utilized a VCA that's no longer in production (Valley People, I believe). Anyway, it was a very well-liked VCA a while back, and many will swear by the early 501's as being great sounding little units at any price. And you can include myself in that group.
Note the picture on this one:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2538795992&category=23793
See the toggle switch to the far right? This is one of the good ones, and you should snatch it up if you're in the market. $70 is a steal. Kicks ass on bass. It's better than the Behringer Composer (and most of the plugin comps you might have for that matter), and will probably last longer, even though it's a good deal older.
Now look at this one:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2539417345&category=23793
See? No toggle switch -- it has a rectangular power switch instead. Not as good as the eariler model. Keep looking for the toggle switch models.
The Symetrix 528 is another beast altogether. It's basically a channel strip in a box. Has mic pre, EQ, de-ess, and compression all in one. Don't even get me started on this one. It's just a step above any of the other budget channel strips out there, without a doubt. And that includes the Focusrite platinum thingies, dbx silver, and Joemeek whatever. Probably 90% of the voiceovers you've heard on TV and radio spots over the years have been run through this guy, by the way.
And it's very upgradeable. Some well-published mods are out there that can make your old, budget 528 in to professional-caliber piece of gear.
www.audioupgrades.com being one of those routes.