I guess it depends on your definition of cheap.
For about $140 the gf 460gtx is a great buy, a little lower down the radeon 5750 is quite good bang per buck, further down the line again and a radeon 5670 or a gtx250 are quite reasonable. Bare in mind though the gtx250 is only a DX10.1 card if that means much to you (although will be faster than the 5670 and on occasions the 5750, but using a DX10.1 path as opposed to DX11). If youre just wanting a budget card power consumption/power supply arent really an issue.
