Honda Hop up!

My first bike, a C200 Honda 90, arrived in a couple of bushel baskets and among many other things required a cylinder rebore, the dealer suggested a stock CB160 piston, which qualified as a hop up, the engine capacity went to a whopping 106 cc. 
These kits would have been the next step except for price. My project was already beyond budget at that stage of my youth, the bike cost $15, piston was $4.80, rings $2.40 and I can't remember how much the boring cost.