Tint price is very regional.
But the price is determined by the quality of the product and the quality of the install.
Better installs almost always charge more (because they're good!). Some people think all tint is the same, but there's a lot of difference to it.
A $120 tint job with a "lifetime warranty" sounds like a good idea, but is it a manufacturer's warranty? If it's in-house, is that guy even going to be around in a few years? What specifically does the warranty cover? Does it cover color change (turning purple), fading (getting lighter)? They are separate things. While you may be better off spending $200 from a good installer with a manufacturer backed nationwide lifetime warranty (in case you move).
I recommend reading this thread:
http://www.8thcivic.com/forums/inside-out/54009-how-you-can-pick-good-tint-shop.html
Also, there's several types of window film out there. Dyed, deep dyed, pigmented poly, metalized, full metal, and ceramics and complex atomic stackings. All have different good and bad points. Some of the high end films reject more heat than most "limo" films!
So the price is the last thing you should ask about!