Just adding info for your decision making process: I just purchased a 2010 Prius II with 19k miles, and had the dealer add a modest tint all the way around (except windshield of course) for $360. It was a B MW dealer who re-sold the car, but their work is impeccable.
Dealer did the tinting before I bought the car. They charged $395 on the sticker, but I ended up getting it for free.