I bought a almost brand new 'New Age' Pit bike for $250 after some dumb *** broke their collar bone. Just check craigslist, and shit like that. Some dealerships have old stock that they want to get rid of so they'll let them go for **** near wholesale prices.
EDIT : I also got an old 'broken' KTM mini bike given to me that some guy was going to scrap, 'cause he couldn't get it running. I spent around 30 minutes, and $5 all together and got it running great. I just had to buy new flaring for it, and it's a better bike than my pit bike.