It's not worth it. If you're in SF, you need a much larger motor. And one that IS NOT mounted on front suspension! What were they thinking?! I bet those forks are even aluminum. The battery won't get you far on your hills, either.
For that price, you could get a motor (hub or otherwise) that will provide a lot more torque and a battery that will actually last. Mount it on your favorite bike and you're good to go.