Sounds like a fair price, assuming it's solid and all there. Make sure the gas tank isn't rusty on the inside.

I have an early 70's (I think) Jawa moped and I was continually fighting with rust inside the tank clogging the jets in the carb. Tried some magic rust converting/coating stuff inside the tank, didn't work. Added an inline fuel filter, got clogged (by little pieces of rust) after a few minutes. Tucked it in the back of my parents' barn and haven't touched it since... I check for a replacement tank now and again. I think it would be fun to have the moped with me in the city for times I don't feel like riding a bicycle, but I doubt I would actually use it much.