Sapphire HD6670. $65 ($15 rebate)http://www.newegg.com/Product/Product.aspx?Item=N82E16814102988
Thats the lowest end card worth buying unless your just after more display outputs. That being said, expect to lower pretty much all the settings and to run at 720p if you want a playable FPS.
Only card available lower than that is a GT210, if your after gaming performance and cant afford the above, stick with integrated graphics.