As for the transmission, If it says "Puch" on a kind of rectangular (actually, flat hexagonal) cover on the right side of the engine, It's a two speed. If it's just flat with a protruding circle, it's a single speed.
If it's in good running condition and not too scratched up, it's worth much more than $75. I would say if it runs good, $200 - $500 depending on the condition of other things. If it doesn't run, $75 -$150 depending on condition.