All depends on what you class as cheap.
I had a toss-up between 7300GT which is really cheap and 8600GT which is what I went for in the end. 7600GT seemed too expensive for something normally half the performance of my 8600GT (which I got from Amazon).
Of course if you really want high performance and native resolution, that rules out cheap entirely. You want at least
a 3850 at which point you might as well just stump up the cash for a 8800GT else you stand to lose a lot of money selling on quite an expensive card.