Well, the official first party guitars are out now(for Wii and PS3) in the US, and they cost $70. Kinda insane for the Wii guitar's price considering two things.
The Wii bundle normally costs $90, and the PS3's costs $100. A $10 difference, so you'd think the guitar's price would be cheaper. But there's more! You also use a Wii remote in the Wii's guitar. So that must make it cheaper to produce, no? The remote takes care of the wireless and the tilt sensing so it should be cheaper. What's more is that you NEED the remote for it, which means if you don't have another one for use with the guitar you have to also make a $40 purchase on that. Something you don't have to think about or do with the PS3 one.
The alternative, which I did, was just to buy a third party guitar that's out now. The Nyko Front Man guitar. It comes in $10 cheaper than the official guitar, and works just as well. And because it's third party, there's a possibility that it COULD work on Rock Band for Wii when it comes out. I doubt it'll work, but there's a possibility.
Anyways... [/rant]