You can give these guys a call:
https://www.metroscreenworks.com
(800) 413-2579
No idea if they're going to be any cheaper than the $700 quote you already got, especially if it has to be shipped.
I don't think your quote is unreasonable, all things considering. You could try building one yourself if you're really wanting to try to keep it under $400. I don't think you're going to find someone to make one for that price.