id say 550-600 mate.
depends on how quick you would like the money..
love motocross myself but be warned its a costly job, aspecialy if your going 2 stroke
mew piston ever 16 houers big /small end bearing
new clutch every 25 odd houers
fuel oil,,,dont run on any cheep tesco crap.
then theres the falling off part..oh they do like to brake them selves
mate of myn fliped his at about 15 mph pratting about, cost him nearly 250..
still good fun though
i just prefair to keep my limbs the way they are now days and go round the countryside at a slow more quiet pace.