I got a Guitar Hero World Tour Guitar [IMO it's the best of these "plastic" guitars, RB2 one is uncomfortable] for 25 dollars on EBay Brand New. That's what I would do If I were you, I don't know about the drums thought I dont have any. XD
But since you want the full set, I suggest GHWT set. You can probably find some for under 100 out here on the internet.
http://www.amazon.com/Guitar-Hero-World-Bundle-PlayStation-3/dp/B001ABN82K/ref=sr_1_3?ie=UTF8&qid=1249683548&sr=8-3
GHWT the game is not good so your better off selling it.
On my PS3 GHWT guitar and drums work with RB1 and RB2 so it should be the same with RB:Beatles

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