Hi ish maintenance requirements , used bikes can be abused money pits , lots of fun off road not so great on the road Magnet for thieves, What were you planning to do ? Green laning or competition??
Don't give into temptation for a 450, get a 250 4 stroke, more than enough for green laning and competition. A Yamaha WR250f is what I ride, very reliable, quick and great fun to ride.