used 4890 might be a nice fit, I think they can be had around $100.
Not sure where you guys are finding 4890s for $100 as I just sold 2 for $155 last week. But if you can find one for that price, then it'll be the most powerful card of the bunch.
Otherwise try looking for a 5750 1Gb as used 5770s are probably more around $125~
After that, the GTS 250 is a pretty good choice also.