I was going to go the sportbike wheel route.. But realized how much work it was going to be...
then one day while searching craigs found a set of Rad hub, excell wheel SM setup off a DRZ400 local for CHEAP. ($300 the set) with tires... as the guy crashed the bike (not with these wheels on it), and needed money for hospital bills... NOW, and his buddys were selling everything off..)
I was surprised how LITTLE work it was to make them fit..
One quick pass on the mill on the sproket adaptor plate, to make it thinner (minimal ... was like .050")
and new wheel spacers.. that I just ordered from Rad (wasnt worth dicking with it for $15)
and it all bolted on..
there is a few writups on Supermotojunkie.com on making sportbike wheels fit CR500 and KX500's...