2 years ago I bought a off road skateboard with a 43cc motor in it, and it was alot of fun. I sold it because it was a death machine, you would basically be doing 60kph with very little control. I paid $180 for it off ebay, I sold it for $250 and saw one of those things but they were called dirtsurfers. So I bid on one but never won it, it sold for $220.
Apparently they are fun to ride once you have the hang of them but are still a couple of hundred dollars of death, as they also had a 43cc motor in them.