Sell your gas car and get a used diesel VW. Cheapest way to turn a 30 mpg car into a 50 mpg car.
My uncle in Denmark has a small diesel station wagon. I drove it about 8 years ago. About 1.5L turbo diesel, the size of a Subaru outback, drives like any other car including plenty of power, and he gets around 50 mpg. Impressive, but US diesel gas still isn't good enough quality to import. There's your conspiracy, why we have high sulfur low quality diesel when Europe has had much cleaner burning diesel for well over a decade. Our answer is small displacement direct injection turbocharged gasoline motors, but they're still behind the latest diesel motors in terms of efficiency. And we still don't have them, because our diesel fuel quality isn't where it needs to be, so those diesel motors can only be imported if they have additional expensive tech to clean up the exhaust.
There's a conspiracy theory you can chase around all week, if you like

It isn't very popular though, because people seem to agree on the basic facts which make it a rather boring, even if true, conspiracy.