Now to actually answer your question...
Walmart, Target, K-mart stores all have buying power in volume. They pay $16-$20.00 for a $100.00 retail bicycle.
The Chinese engine kits that we buy cost $22.00-$28.00, again based on volume. So given the volume pricing, in theory you could build a nice motorized bicycle for $50.00 or so. All you have to do is buy several million dollars worth of inventory.
The mini-choppers are built entirely in China and then sold to dealers. In quantity the dealers are paying 25-30% of the retail value that you see!
So, in wondering how they can do it so cheap!...It actually goes to another level that will leave you truly astonished as to how they do it...because the retail mark-up is huge.