> Expand to the other major chain restaurants and source your pricing from Mechanical Turk (except for the dollar menus of course). I'd take a few precautions to validate the data. For example, you could put up an HIT to get Burger King's entire menu and have 5 people complete it. Compare, lather, and repeat. But I see that as only the first step.

I have an API that does this automatically for you, http://houdinihq.com. I'd be happy to help the OP if there's an interest in doing something like this.