Those are AWESOME. I've looked at doing one on my MTN bike, make a mini dirt bike of sorts. All different types of configurations you can go with, front hub motor, rear hub motor, DUAL HUB MOTORS for 2wd!!!!!! The batteries are where it gets expensive, they can easily go for $800-$1000 or more. At our shop we sell a few production e-bikes, not the kits, and they are a little more tame because they have to be restricted to under 20mph to be still a bicycle and not a motor driven cycle. There are people that build their own kit ones that top 50+mph and can cruise for 30-40 miles on a charge. I have a feeling they are going to be HUGE in the future, once the price of the Lithium Ion battery goes down.