If you Mobo supports PCI-E and if you really wish nVidia Ge Force cards that cost till 100$, then i guess a 8600 or 8600GT would suit just fine, while 8800 series would be the best choice, but that`s additional $.
I play the game on 800x600 graphics maxed on a EN8500GT. So you might consider that aswell, but i don`t suggest. Could be about 50-70$