If he's driving a 4X4 truck, I'm betting he's getting maybe 10-14mpg. He probably has a 25 gallon tank or more. Lets say $4.00/gal right now. That's $100 to fill. A Cruise or Jetta will be getting around, lets say 40mpg. Most small cars have about 10-12 gallon tanks. That's $48. If you use half as much fuel and pay half as much money to fill, but, you'll go 4 times as far, my math says you will be saving money. I could be wrong. Over the lifetime of the vehicle you will be using half as much fuel and money to drive it. Am I missing something? Of course these are small cars, larger Diesels will use more fuel but much less than gasoline.