By the way, consider build vs buy. I considered this model from farbike.com. It's $700 shipped, and has a 350W geared rear motor, 24v battery, disk brakes, new tires, and a front suspension. I spent $500 for a similar motor but a bigger battery, and by the time you count the new tires, tubes, new front wheel, brake upgrades, and a front fork with suspension, I spent more than $700.

It all depends on why you are doing this. Just a hands-on hobby for me, and also recreational riding.