Unless you already have the equipment. I definitely regret selling what I did when I did (since I let my drums go for $30 and who knows how much I could get now) but if you play a single instrument, all you need is that one accessory. Even though the mic is easiest, its probably the worst (imho), I suggest putting out the money for at least a guitar or just not getting any of this sort of game. The guitar is the best imho (and you get 2 instruments in 1, guitar and bass).
There is also a game called Rocksmith I've been trying to get on here (always get last minute outbid, no longer do I hold my breath). If you have your own guitar all you need is the game and a cord that is generally provided (but I wouldn't suggest buying that one sans the cord, I guess its expensive to find the cord on its own, almost as much as buying the game new w/ the cord).