I just got a quote from HL parts to replace all the windows in our trailer to dual pane.
It was $3,800 for 11 windows plus a guess of $600 for shipping./
I did find these two sites but have not contacted either one
http://hehr-international.com/Window%20Products.htm
http://www.motionwindows.com/prod1800.php
I cant imagine the price would be much better. Average window price is 345 from Heartland. Sounds reasonable until you multiply by 11.
I did not get indivual prices. The little bedroom windows are probably pretty reasonable. The 3 big picture windows - probably not so much.
I do know installing them is not that hard. I had to remove a couple of windows on another unit once. Just a couple of screws and cut the caulking and they pretty much fall out.