If you really don't want to pass over that $250 price point, then here:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814129230
Don't get an XFX card. I won't go into the details, but I do urge you to go to XFX's website and read their updated RMA policy....which they did not inform their customers of, plus they still have it listed incorrectly on newegg's website. Most of their cards are NOT a lifetime warranty anymore.
Anyway, a 7850 with a nice heavy overclock of 1.1-1.2GHz will easily keep up with a 7950 with a light overclock.
Again, you're not going to get that kind of performance with Nvidia in that price range. You're just not going to. Plus you're also going to be drawing at minimum 100w more per GPU with Nvidia in that price range. 560Ti is about 180w TDP card, 570 is about a 225w TDP card, 480 is a 325w TDP card. The 7850 (which beats all of these) is a 90w TDP card.
To equal a 7850 heavily overclocked, you're going to need a GTX 580 heavily overclocked (probably under water). Two card systems, again you'll be looking at 580 SLI (which will require a 750+ w power supply) just to compete with the 7850 crossfire solution (which would run fine crossfired off a good 450w unit).