5870 vs GTX295 (How much extra would you pay?)

[wonton1017]

I have been googling for the past few days and found many reviews and comparisons between the 5870 and gtx295, it seems like the GTX295 is a little bit better.

I have a choice of trading my gtx295 co-op for a 5870 + cash, how much cash should i be looking for?

I am also thinking about trading the 5870 for a 5850 + cash later on when i find another deal on a 5850 so i can do crossfire, how much cash should i be looking for this?