Quite a few of us on here have made frames and stretched blackout cloth over them.
It's cheap and does a good job. In my case it was a stop gap until I got a better screen, but it does such a good job, I've not upgraded it in over two years now.
If you need higher than unity gain, a proper screen with appropriate material will be needed, but if you want a less than unity grey screen, you can paint the home made one.
You could always go the Screen Goo route for approx $100 and get the best painted screen for your money -
www.goosystems.com
Gary.