Yikes; GTX 280 really expensive (but still has better performance than 9800 GX2.) Still, I'd wait till the price drops (unless you're getting a GTX 260.) Still, consider that the Geforce 8800 Ultra several years ago was retailing for the same price as the GTX 280.

Personally, I think that right now the best bet for your budget is the Geforce 8800 GTX (the Ultra is too expensive for only 10% preformance incarease). If you have a big budget, the Ultra or SLI GTX are your best bet (unless you want to wait for the 9800 or buy the 9600.)