It takes about 3 hours to build an SSV from scratch. This includes the knob, cutting and finishing the housing. Some of these things are not done in the house anymore, but still is done and still require the same time.
There is no way a person could build an SSV for less money than we sell one for. Maybe they could somehow do it, but they would have to possess a lot of skills as well as own a lot of tools, and for those reasons, we say there is NO way anyone could build one for less than we sell one for.