changing the timing belt is pretty difficult if you don't have alot of experience turning a wrench. You might also need tools that you don't already have. As mentioned before, the most difficult part is getting the 19mm crank pully bolt out. That sucker is in there tight. I still have not gotten mine out yet (I need to buy several extentions so that I can use my breaker bar)

I would guess that taking it to a mechanic will run you 3-400 bucks...