The motor at HF is $120, their trans is $120, the CNC sprocket, $60, the CNC motor mount $60, that totals 360, the kit includes the throttle kit, gas tank, and misc stuff, that is worth more than the $19 that is left.
The wide crank, that will be needed and is not included. Still cheaper as a kit than by buying each component separately.
Personally, the 79cc is more than enough for a bicycle, if you want the 212, you would be better off looking at a motorcycle. The motorcycles have better brakes, stronger frames and are designed for that kind of torque.