If it's not too much past your budget, the $94 Radeon 9600 is probably the best deal
http://www.newegg.com/app/ViewProductDesc.asp?description=14-102-289
It can overclock to a little over Radeon 9600 Pro speeds pretty easily.
You don't want to get any of the Radeon SE cards because they have half the memory bandwidth. If you look in that budget roundup, you'll see that in UT3K, the GeForce Ti4200 and the Radeon 9600 are the same speed, but the Radeon 9600 SE is half the speed.
If you want to get a used GeForce Ti4200, that will be good enough for you (I'm still using a Ti4200 myself). I can't believe a GF4 Ti4200 is still so expensive -- I paid $119 for one in March 2003! Anyway, keep in mind that the Ti4200 is a DX8 card with pixel shader 1.1, and the Radeon 9600 is a DX9 card with pixel shader 2.0. The Radeon will last you longer.
Here's that budget roundup:
http://www.anandtech.com/video/showdoc.html?i=1933