Why pay the outrageous price from the BMW dealership for a replacement window? Why pay for a whole window when only the plastic is bad?

Most E30 BMW's had a window that is sewed and glued on. When you go to the dealership, they will sell you a window for close to $300 and an "install kit." I'm selling the exact same thing, but it is not from BMW. I include the same tools that were in the install kit. The instructions indicate that you hand sew this new window into the old holes. It is a 2+ hour job that is best handled with two people.