Not that I have been looking much, but I think that the prices are fixed at that mark no matter where you go. I can only suggest possibly Wal-Mart or EBGames and hope for a few bucks off.
Yeah, I couldn't find anything else either... by the time I totalled up the $300 for the console, plus the $180 for Rock Band 2, plus Guitar Hero Aerosmith for more tunes and the other guitar, and taxes, we were coming up on $700. It's fun, but not that fun. Plus, I don't know anyone who hasn't had to replace a guitar already.
Just don't think it's that fun for us, we'd never use the console for anything else.
So instead she's getting an iPod (eww... Apple stuff in the house - well, I DO have a MacAlly USB hub
) and I'm getting a duck blind. Much more useful for us.