If you compare the initial price of GT200 series with the highest guestimate of RV580... they are still cheap.

On realease:
GTX280 U$S649
GTX260 U$S449

HD5850 for U$S299 and HD5870 for U$S399 is cheap for next gen. high end cards. For a few months they'll be the fastest sigle cards out there by a huge margin. I think AMD will cut the price after GT300 is launched.