By the law of supply and demand, it will again get cheaper. Once we get to a point of near no dependence on fossil fuels, the price will drop as demand drops. Later as gasoline burning vehicles become obsolete in the same way that rotary phones or collectables, people will either be giving gas away or charging a fortune in comparison to today's prices.
But it will go down. We likely won't see it, though. The progression of electric and alternative fueled vehicles isn't fast enough.
Price will go down only as long as supply remains high. When demand drops off, producers have learned to limit production to keep the price in equilibrium.
Heck even the Arabs know this and realize that from their end. A certain price per barrel of oil prevents the production of alternative fuels and competition, and over that, causes it. So they regulate their flow to keep the price high, but not too high.
Diesel is not a viable option in the long run. Still runs on the same stuff, just less refined.
Electric is certainly an option, but batteries don't like cold and become inefficient. The new storage mediums like LiPo and the like, even more so. Then there is the range on an electric. Fine around town, but no long trips. The Hybrid seems to answer both those issues and have a backup fuel source when you run out of batteries. I like the idea of the "plug in" Hybrids where you top them off at night.
NG seems to be catching on in some parts. I heard there are big in Utah. The Fuel is less than gasoline, every house has it. You just need a compressor in the garage to pump it up and pressurize the tank with it. There is a company that makes one. Over all, if you had 2 vehicles, didn't mind the initial investment, it would save you money. There are also a number of dual fuel NG/Gas vehicles available used @ Government auction.
I saw an MG&E truck yesterday with a HYBRID sign on it. It was an IHC with a Utility box on the back instead of a Load box.
