Don't know how it's set up on Suzukis, but powervalves can be somewhat expensive, depending on the part...
The bigger question is WHY in the world would it need one? I've never needed to replace one. Kinda hard to destroy one, and if it is then that's probably not the only thing messed up in that motor.
As for difficulty, if you can do a top end you can replace a powervalve, at least if you have a shop manual handy. If you can't then shop time is typically about $75/hr.