I wonder how much $$$ the prequels would have made had they been any good (ie. Lucas got someone else to write/direct/create them). The demand was insanely high for TPM, and as the movie sucked dead bears, it was an opportunity that will likely never come around again.
Easily 1 billion for TPM if it's above-average, and the sky's the limit if it was of the same quality as SW or ESB.