Yep, buy it from a scrap yard and rebuild it...
Seriously though, you could place an ad asking for someone who wantes it out of their garage... ride your bike around the 'hood and look into the open garages to see if there's a ped hidded in there looking for a new owner
It is really hard... but I might approach it like "finding a lost cat" put up flyers, saying "I need a moped" Will pay top dollar (50$ tops). If you know someone with a ped call me.
If it cost 40 bucks to sell the ped in the paper classified, people might not think it's worth it for a 50$ ped.
I doubt you'll have much luck w/ your cost window. Heck, you'd be pressed to get a 10 speed for that