The Problem With Flying Cars

The problem with flying cars is fuel efficiency. From what I understand, they get about .125 nautical miles to the gallon. I'm pretty sure we'd have flying cars by now if we had an alternate fuel. I mean, the mechanics are probably simple enough, and we've got light enough materials now that the cars could get off the ground. We just need more efficient fuel. If I was an engineer, I'd be all over this, but alas, I'm just an idea man. And I have no money. So I'm selling this idea. Shall we start the bidding at, say, 50 million dollars?