Window from Prevost should be about $350 with free shipping, plus a tube of Sika, about a 1 hour job- FWIW
Do you have an account set up with Prevost? Do they even have you in their records as the current owner? If not call with your Vin # an get that set up. Mine is an H3-40, I was quoted $4 hundred and change for the same window and yes as said free shipping! Pull the window yourself and either take to a glass shop or buy new, a new tube of Sika will accompany the new window from Prevo.
A lot of Prevost owners will do the glass replacement themselves. It is a simple but a little time consuming process. Go to the Prevost Car web site and under maintenance and parts you can pull up the shop manuals for your coach. It will show the window replacement procedure.If a local shop cannot repair the thermopane windows and alternative is to use a single pane heavy safety glass which is what the toll window is on your coach.