Over the years I've seen a couple of the Harris or ROC 500s come up for sale. Usually go for around 15K. Bet spares are a bitch to find.
Any how I think a sorted RS250 is all you'd need 90+bhp will get me from A to B quick enough. sh*t I can scare myself on my old moped and that can't have more than 10bhp.
Before you say it ..I know that we onky build em cos we can so I'm up for the 500/1000 two-stroke project........who's money we spendin?