If you sell your other cards for a combined $50-60, Then you would have $150. I know that Microcenter has a brand new EVGA 580 GTX for $145.99 if you can order from their website for one of those or if you live near one of those. That would be a remarkable bang for your buck. The 580 GTX's dropped again since the release of the 980 GTX to that pricing. So that would be your best bet.
I know that 580 GTX's sell for about $100 used on Ebay. That would be my recommendation given your price point for solid performing card.