Do realize these parts kits have some very cheap parts. Like the crank and pedals. Mine are cheap and the bikes don't pedal nice at all but getting a good one is expensive relative to these kits. The pineapple bushing is crap compared to a CNC adapter but that will cost you $70-$100. You can buy a good crank set but again $100. On and on. I priced out a bike I would like to build just to see what the ball park numbers are and I hit $1000 fast. That's with a 4 stroke Chinese motor and a standard belt drive transmission.
I have an unknown kit build, one from Gasbike and one from King's motors. All the parts are basically the same except the transmissions.