Sorry, I apologize for the lateness of my response.
I always keep forgetting to "subscribe" to these threads...
Anyway, I researched window tint and decided on the 3M Prestige due to it's quality, etc. Then I just went to the Find a Dealer part of the website and found someone local to me. I went over there and told them how much I needed and walked out with it.
One final recommendation. Yes, you can get stuff that is less expensive and still have it do the job. I wanted something guaranteed not to turn purple along with the other qualities noted in my original post. I don't want to have to tear it out and do it again. When I thought about it originally, I didn't want to spend $220 on "window film". The dealer told me point blank that it was an excellent investment, because when they get trailers for trade that have sun-faded furniture/carpet, they immediately decrease the trade value because they know it will be a harder sell to someone else.
Whatever you do, DO NOT buy the stuff you can get in a regular Auto Parts store (Pep Boys, AutoZone, etc). It is thinner stuff that is harder to apply, scratches easier, and will be more headaches than it is worth.
'07 GMC Yukon Denali 6.2L 6spd
'06 Salem LE 27BHSS
Prodigy Brake Controller