Cory: let me know how that tint looks 5 yeard or so down the road. Who knows, it might be good quality stuff that doesnt fade and/or turn purple, but who knows?
Quality of film is every bit as important as quality of the installer. Call around to pros and ask them what kind of film they use and what kind of warranty they offer with it. LLumar, Madico, and Suntek are gonna be your better films out there, and will hold up well and wont fade.
As for doing it yourself: all you have to do is miss one bubble, get one tear, or one crease, and your tint job is ruined. At that point, even if you took it to a pro, the film probably won't match, and it wont match enough that you will be able to see a difference. 30% gray from Madico and 30% from Llumar don't match one another, so im betting that most of the other brands wont match either.
Save yourself some time and headache and eat the cost of having someone do it professionally. $170 is a VERY good price for tinting that car. And as professor said, a professional shop is going to charge you at LEAST that to remove bad tint, PLUS the cost of tinting again.