I've been building a small car that "beats" the regulations. I built it as a 3 wheeler. Here in NC if a vehicle has less than 4 wheels and weighs under 1500 lbs it is technically a motorcycle. You can enclose it, heat it, run A/C, ect and it is still a motorcycle. My motorcycle insurance is $38 for 6 months. The "car" has a 1800 cc 94 hp Subaru flat four, a 5 speed transaxle, and the whole thing weighs a little over 800 lbs. I'm still working on it but I expect over 60 mpg out of it.