Guess I'm not surprised, you go to a hotel and get "resort fees", the airlines charge luggage fees, on-line purchases have shipping and handling, and don't forget those dock fees. Even a visit to your doctor, lawyer, CPA has a parking fee, in Los Angeles it can be $20 or more. Then there are disposal fees for tires, oil, batteries, electronics, and other things, usually mandated by ordinances. I guess when you ask how much you must insist that any additional fees be disclosed. Perhaps in the estimate you should include a statement with your signature that says; "not to exceed...."
I have not had CW install anything in years, but I would be interested to know if the estimate or service contract asterisk plus additional fees.
Just wondering.
Happy Trails.