I agree most shops will do it for little or no charge if you have them tint it for you. I do 85% of the work on my car, have removed tint from cars several times, and I would not want to do the back window ever again. When I had my 300E tinted two months ago, they removed all stickers and tinted 4 sides and back window with metalized tint for $120.
If you are sure you want to DIY, check your local car store, auto section of superstore they will have tools and solvents that can help you.
peace
don
