Well, first of all its not *very* cheap unless you are travelling in trio. But If you don't own a car or hate driving or want to *see* US of A in short span of time or can't carter visiting parents this is of the best site:
These are typically Chinese run travel tours mainly concentrated in East and West coasts. I've travelled on their Washington, Las Vegas tours and its pretty okay. The travel, loading is covered, we need to pay for the food and the entrance tickets.