Although not windpowered - check this badboy for $200.
Its 50cc and does 40kmh....
great for no wind and no surf days!!!
you could remove the engine and adapt the mounts to fit a mast foot easily.
the real axle steers with suspension like the front. (same system as found on mountain boards) so it would deffo work.
plus sides are the wheels and tyres are an inch bigger than convensional mountain boards (less bogging down in sand) and board is longer than a conventional mountain board conversion, so will handle more power and less death wobbles!!
plus its much cheaper at $200 notes and you get a free engine.