My experience has been that a Home Depot orange cart is scientifically designed to hold $400, no matter what you fill it with. lol.
I ordered my windows from Callen Camper.
The Callen Camper Company They are a small outfit in CA that builds custom small trailers and pickup bodies. They are setup to buy the windows direct from the mfg. for their builds, and I think they just sell the windows retail to keep their volume up enough to keep buying direct. She was able to get me just the size and configurations I needed. They can have them made specifically to order, and sometimes they have a little better deal if something is on the shelf in the neighborhood that you need. You'll need to measure your wall thickness down to the nearest 1/8" so they can get you the proper trim rings. Mine were a perfect fit, no hassles. Like I said, a little pricier than the surplus stuff, but worth it.
Some of the manufacturers will sell direct now too, times are tough all over.