Projection Screen Paint
I am not sure projection screen paint on the wall is a replacement for a nice motorized projection screen. However, if you still project onto a white wall, this somewhat inexpensive solution maybe for you. Inexpensive when compared to some screens, expensive when compared to paint.
There are a few different options. MPW 10 supplies enough paint to paint on a screen and thats it. For a little more contrast between your wall and painted screen, MPW 20 provides magnetic border and paint. MPW 30 is the same thing as 20 but provides enough paint for the entire wall.
If anyone gives this a try, let me know how it works for you.