A Radeon 6770 is $59 and way above anything else in the price range http://www.newegg.com/Product/Product.aspx?Item=N82E168... I can't find anything under $50 I could recommend unless you look on Ebay for a used 4870 or similar as long as the power supply can handle it, they sell very cheap all the time in auctions.
HD 6570 If not try to look around local stores for some used graphic cards. Or if you still want something new then go for the HD6450 but bare in mind that the HD6450 is out of the "Gaming" league. and the HD6570 is a decent entry level solution for all games.