Last year, Sean Donahue, a 37-year-old marketing director at a branding firm near San Diego, attended the Consumer Electronics Show in Las Vegas, where, amid virtual reality goggles and 4K televisions, he saw a design that struck him as truly futuristic. “It looked like something out of the movie ‘Gattaca,’ ” Mr. Donahue said. “As a nerdy tech guy, I was enthralled with it.”

The invention was a prototype of a two-seat three-wheeled car built by Elio Motors, a Phoenix-based start-up founded by Paul Elio in 2008 with the mission to create an inexpensive, American-made, fuel-efficient vehicle.

The $6,800 Elio uses the relatively ancient technology of a gas-powered engine. What makes the car seem advanced is the slender, rocketlike body made possible by its tandem seating design. Aerodynamically curved, it can travel 84 highway miles on a gallon of gas, according to its maker.

Perhaps in a gambling mood, given that he was in Las Vegas, Mr. Donahue plunked down $500 to get his name on the Elio waiting list.