The guys from Inventgeek made their own LCD projector for less than $200, ideally for viewing movies on a big screen. At the end they were even amazed that it was such an easy project.
The principals that make projection in general possible are very simple in concept. You need simply 4 requirements to be met: a light source, the brighter the better; some form of imagery medium, film or LCD it's all the same conceptually; a focusing mechanism to help provide a crisp image; and finally a display medium. There are many ways of accomplishing each of these requirements. We will be glancing over them and providing some examples that could fulfill the requirements for our LCD Projector.