1. The Screen
The screen may seem like the most daunting aspect of building a backyard theater, but it doesn't have to be so. While inflatable screens designed for outdoor use from Open Air Cinema start at $599, David Banks at GeekDad put together an excellent guide for building a portable outdoor movie screen using materials that will cost you around $125.
2. The Source (Video Projector, DVD Player, Speakers)
If you're simply looking for the equipment to host a one-time outdoor movie night, all of the equipment can be rented online from companies like Source One Rentals, who rent the projector, speakers and DVD Player in packages that start at $199.
Visit BackyardTheater.com for tons of great tips & tricks and to see some of the other ways people have built backyard movie theaters!