I always liked this 80s model....
http://imcdb.org/vehicle_3895-Volkswagen-Rabbit-Convertible-Typ-17-1980.html
I know for a fact the 1986 version without AC or power anything, and a stick shift got 60-65MPG on the interstate. I have no idea what it was officially rated for.
Couple problems with the Sprint. First, the testing standards were different, and it would probably get more like 37/42 today.
Second, you could ball one up in your hands like a sheet of newspaper. Even little cars today have to meet much more strict crash standards, which leads to lower economy numbers.
I had one of those. More like 45 city and 65 hwy