Gamestop seems to have rock band controllers for 25 in store. I've seen several, but haven't had time to look more closely at them to see if they are RB 1 or 2. I don't know why there are so few of them new out there.
That $10 Explorer guitar is pretty decent. I prefer it best, but it's wired, so I didn't bother with it.
Wish I had, now I have a shitty GHWT guitar with a broken upstrum.
Edit: Avoid most used GHWT and RB1 guitars, as the strum bars are shit. GH3 (with a permanent neck mod) and GH2 guitars are best though, as those strum bars are like ing tanks. I can't personally comment on RB2 guitars.