No, I'm not kidding! It's true! It's cheap. It's easy. It's actually pure genius.
I came across this one over at Filth Wizardry. In a nutshell, take one disposable plastic tablecloth (found in your supermarket party section for around $2), some sticky tape, textas and a good dose of imagination and you're off and running. Hop over here for the full tutorial, and while you're there, take a look around. Lindsey is bursting with great ideas for preschoolers.