I just sold my 5870 for 45$.. have a look ,I see them regularly go for 50$ or less - still a great gaming card for the price, still matches the 6950 unless you are cranking up the tesselation
There was a guy selling a HD 7870 for $65. But looks like it was snapped up. I would look around that range. 7850-7870 or a GTX 650ti Boost/ GTX 660 if you are lucky. Post a wanted ad.