Well, the iMac has to sell for less than a PowerMac G4, considering its the "Consumer" line of Apple's products.
Given that TFT screens are more expensive than their CRT counterparts, it wouldn't be surprising to see the price tag hover in the $1,300+ area. :|
But a GHz iMac would be cool. I hope that they can make it a wee bit more expandable, though. Being able to add 1 more drive would be nice.