If there is window tint already on the vehicle it more than likely will have to come off unless your trying to match it. Removing tint is a process that can take longer than tinting the vehicle. We charge $10 per side window and anywhere from $50 to $150 for a big back window. This all depends on how long the tint has been on the vehicle, what kind of tint it is and even where the car has been (down south its in the hot sun more).
There are always exceptions. Some vehicles have a back window that may take more time to tint then others. Some vehicles have deeper side moldings that need more attention. Older vehicles usually need more prep work because of all of the dirt that has accumulated over time. So size and shape of the glass. The age of the vehicle and the obstacles that must be worked around all come into play.
Last but definitely NOT least is the quality of the job. When you call around and the average price for a 2010 Ford Fusion is $200 and you get a price for $125 $150 question their quality and professionalism. There is a reason they are not charging the same as the rest of us and that reason is more than likely quality. Remember they are working on YOUR vehicle!