Screen Material
I built my own from material for sale on eBay. I paid about $35 for the material, and they included frame plans (really just 1 x 2s with metal corner brackets). The material was attached with a staple gun (with two helpers keeping tension while I stapled), and the overall dimensions were 7' x 5'.
I was pretty happy with it for a while -- especially the price/performace ratio. Then I acquired a portable, tripod-style screen from DaLite with their Cimema-whatever-it-is coating. It has a gain of 1.5. Since I only irregularly need this screen (8' x 8', ~$350) on the road, I rigged a support system for it in my HT. The quality difference was quite appreciable, in fact I was a little embarrassed that I actully liked the homemade screen before, but there's times when I'm easier to please. The increased brightness and physical resolution on the screen were the standout differences.
Look at it this way -- if you spend <$100 building your own screen and you're happy with it while you're fine-tuning your audio setup, etc., and taking more time to evaluate other screen options, you probably would be OK.