Nvidia's next step up from the impressive but pricey 8800 series will be the 8900GTX and 8950GX2. As the model numbers would imply, these are performance class cards and come with a performance class price. The pricer of the two, the 8950GX2, currently rumored to be a dual-GPU solution, will come in with a massive price tag of $600. The 8900GTX will be slightly less at around $550. Indeed, it seems the high end cards from both camps, whether ATI/AMD or Nvidia, are carrying enormous price tags that make even the PS3 look cheap.
These prices are only estimates, but given the cost of the R600/2800 series cards AMD has planned and the comparable specifications, it sounds about right.