If the $100 includes the price of the glass, it's a deal. Have them do it. Otherwise, depending on if the guides are already bolted on the bottom of the new glass, it can go one of a few ways. The easiest is to remove the guides that are pop-riveted into the glass at bottom. I have found it is easier to drill the rivets out...some people use a cut-off wheel. I went through a few cut-off disks on just a couple of the rivets. The rivet size is 3/16" I think. So, drill straight and carefully with a smaller bit. Then, CAREFULLY slide glass into tailgate (make sure you have the regulator arms all the way down first). Once in, and you may need a friend to help secure the glass while working, either bolt or pop rivet the guides back on the bottom. Then hook your arms up. Good to go.
Snowman74