Just a few ideas to throw into the mess:
What about plug-in hybrids? 40-60 miles on all electric range (which satisfies the average person's daily driving needs), you roughly pay about 7 cents a mile when running in electric mode; beyond that the car would run as a conventional series-parallel hybrid.
The technology is available (although this claim is pretty controversial between the people who R&D plug-ins and car companies). I can't remember the exact increase in overall price, but I think it was in the range of $5-7k, which is about what you pay for a lot of fancy creature comforts that most people don't often use in their car (like the sun roof, or fancy navigation system). Plug-in hybrids, in my opinion, seem to be the best option to displacing the consumption of fossil fuels -- that and it would be a good crossover to going back to all electric vehicles
By the way, to convert the current US fleet from gasoline to ethanol isn't possible, because we can't produce enough crop to produce enough biofuel.
And lastly, hydrogen isn't a miracle fuel, well it isn't a fuel at all. Fuels is a resource you harvest and refine; hydrogen is just an energy carrier, since we need to extract it from the air or from water. It also takes 3 times as much energy to create hydrogen compared to the same amount of gasoline, as of right now. So hydrogen cars may produce 'zero-emissions' but the pollution is just moved upstream. You also lose energy by having to store it in the high pressure tanks. Quite a few problems and not enough time
