RE: buying a new one
I have a 02 YZF 426 all stock its the last year they made the 426 before they went to the 450 and it is faster than a newer 250 and my friend has a 04-05 CR 250 fmf pipe and silencer v force reed valve and mines faster, if you dont mind spending a little extra money get the a 450 the only thing is the lack of your dirt bike experience and the power of a 450 but for a newer rider I think a 450 would be easier to ride than a 250. My bro has a 06 CRF 450 with a white brothers carbon fiber exhaust and rejeted carb and his bike pulls crazy hard. If you would be interested in a bike with a light and electric start the CRF450X is a 450 frame gearing setup more for desert trail ridding with a little less power, stock the 450x is pretty poor in power because the the factory sets the jetting really lean for smog reasons I think, but pull the baffel out and rejet carb its not to bad of a bike, probably close to the power if not the same as a 250