It will probably be the same price scale as XP is now; but specific prices for the different versions is wide and second guessed. We will have to wait for Beta even to know what versions Microsoft is making, at which point an idea on which version will cost what is more likely. I'd guess Home will be about $80.
They have said Second Quarter 2006; May is a possibility but you'd expect Late May or June, possibly Late June if indeed it doesn't slip into Third Quarter.