Picked up a beat Yamaha PW50 for a couple hundred bucks off craigslist. Everything was trashed and needed painted at the least.
I picked up this cheap complete top end kit with new head, cylinder, and piston, for less than price of factory gaskets.
I also decided to go with these brand new set of front fork tubes instead of reubuilding the stock pieces.
At this point you will have a brand new bike for a fraction of the cost. New plasticis available if yours is in bad shape, I chose to sticker up the factory plastic to keep the cost down.