I saw a black one seater automobile with antique car tag looked new but retro in Dunedin FL What year and kind of car is it?
Insufficient information to be able to give you a answer. We could guess but that is really no better than what you know now. Provide a better description.
The black single-seater car that you saw is probably the Volkswagen 1 Litre car. You can check out the image of the car which is considered quire economical by visiting http://www.caradvice.com.au/25172/volkswagen-introduces-worlds-most-economical-car/.