The prices are lower because rumors are that though it'll be faster than the RV670, AMD plans to undercut the pricing on their boards. It will also be hotter than the RV670, but still looks like it will be single-slot; though all shots I've seen thus far are sporting the reference cooler. The interesting news is the quantity available:

"We managed to learn that for the very first launch day, Nvidia got Foxconn and Flextronics to push out a grand total of 50,000 512MB boards for first wave, followed by a smaller number for the week after, and a higher number for weeks after that."