The motor, batteries, and cycleanalyst ran me 2k. if I had another 250 at the time I would have gone for the 20AH battery. Probably upgrade to it in like 3 years.
Its an investment, but keeping up with it is easy as making sure the rest of the bike is up to snuff. eventually the batteries will need replacing, but that shouldn't be for a while.
Right now its quite nice seeing my project come together, I wish it was done already but bit by bit I'm seeing it get closer to what I'm envisioning. Some day there may be a sidecar attached to my bike