Your dealer is trying to take you to the cleaners. OEM glass runs $360 from Tischer. Get the part numbers for the others parts you'll need, and look them up on Tischers site as well(
www.getbmwparts.com) and then call dealers up and have them price match. I had Circle BMW come pretty close to Tischer on door glass, as soon as I mentioned price matching another dealer. Then call up a local glass installer with a good reputation and have him do it for you.