we need more info than that mate, games don't solemnly run based on your graphic card.
CPU speed ? - and how many cores
RAM ? how much, and what frequency?
Hard drives (with focus on the RPM)
and like Rockyjohn said, what games, is it pacman or crysis 2?
what budget do you have? 10$ 500$ ? "not too expensive" is based on where you're from
also, most graphic cards nowadays (the good ones) needs 6pin-8pin power plugins (or mine that need 2x6pins each), so you might want to check if your power supply has that as well.