Here's a video of a homemade electric bicycle. It's pretty much a do
it yourself project, what you see here.
This set up gets him about 20 miles without any pedaling at all. He's using lithium batteries (less weight).
The bicycle itself is 70 pounds. As you can see from the video you can tell it's a do it yourself project (notice the zip ties and battery pack).
These set ups can cost anywhere from $1,000 to $3,000 depending on everything including the bicycle you use, the kit, hub, and batteries.
On this one the motor is in the hub of the wheel (cool). This one here is a 72 volt kit so it's pretty powerful. He says that a 48 volt would be more "appropriate" for just commuting.
This particular bicycle will go about 50 MPH. Impressive!
Watch right here...