ok so here's the gen in the uk:
GameStation are currently selling Guitar Hero 3 for £75 for the XBox 360, a little bit cheaper for the Wii
Game are of a similar price
HMV, however, are selling GH3 for any platform at £60
So, if your buying from GameStation or Game and they wont match the price of £60 then tell em that you'll be going to HMV
If you've already paid out then take your receipt back and ask for credit or a refund if they refuse.