We've featured DIY projector screens before, but as far as DIY projects go they can still get a bit pricey. If you're got a nice, flat wall, you can use this method to create a great screen on the cheap.
Using just a magnifying glass from The Dollar Tree, and some plywood, you can make a DIY Movie Projector using just your smartphone. Includes step-by-step instructions and tips for making it work properly! - Thrift Diving