The famous post-war French moped is still around today- and will cost you less than an electric bike if you can afford the new tyres driven directly by the little engine on the front. When I was a kid, my older brother and his wizard mechanic mate fitted a two-stroke to drive the back wheel of his bike like this. The engine had been salvaged fromwhat is known as a social tandem or social bike, a four wheeler with two seats and sets of pedals. That vehicle was used by the local vicar and his wife on their pastoral duties before they moved on to the luxury of a Bond three wheeler minicar. The reason I mention the Solex is that it is now produced as an electric bike, its folding version described on this site.