I'm not sure if pricing matters that much. People generally buy a new PC with Windows preinstalled. Otherwise normal users don't really go to buy the operating system by themselves separately.
I think the buzz will matter a lot. If it is positive, people will give it a chance, if not they will say "give me my Windows XP back".
And Windows 7 already has some positive buzz going on. I've been talking with normal users who say that they hate Vista even though they never used it but they can't wait to for Windows 7 to launch.