Remember the Geo Metro from the early '90's? In particular, the XFi model got EPA ratings of 53/58, 55mpg combined. And real people acheived these numbers in real traffic and then some. This is better than most hybrids and diesels. No complicated hybrid stuff, no expensive diesel fuel. I think the car only cost about $6000 back in 1994 (which is about $7300 today). Used examples can be had for far less. The Metro was available as a 2- or 4-door hatchback, and even a convertible (although the XFI only came as a 2-door hatchback and a 5-speed). The convertible seats 2, the others seat 4.

Maybe they could bring back the Metro (although it would be a Chevy Metro now that Geo is gone) and even make a Metro hybrid. It could also be flex-fuel with E85. The XFi gets 55 mpg without the hybrid part, maybe it might get about 80 mpg as a hybrid.