This may take a while. This counts as anything from the rock shop, like instruments, accessories, clothes etc. The best way to get this is to use the same technique to 5 star songs in the "One Million Fans" achievement, because the more stars you get, the more money you get. If you ever get an offer to "Quadruple or Nothing" or "Double or Nothing" for five starring a song, and you know you can five star it, always take it. Even if you can only 5 star one of them, you will get 4 times the cash for that one, but nothing for the other one.