Aside from the motor kit which I took off of my mountain bike so I could return the bike to its original purpose The bike pictured below cost me a grand total of $12.94 to build. True if you figured in time at 15 cents an hour it probably cost more like $200.
Cost break down:
Frame and related hardware - Free, Craigslist and freecycle.org
New cables - $3.97
New tube - $3.97
Motorcycle grips - $1.00 yard sale
Motorcycle trunk and Seat back - $5.00
Goofy looking comfortable ride - Priceless.
I scored the motorcycle trunk and had to install it, now the back pack full of tools that I never leave home with out has a place for storage. The 20 inch BMX wheels cruise at about 15-20 mph with a 44t sprocket, with plenty of torque to haul my fat butt up any hill I find. Pedaling for any length of time with out swerving all over the road is near impossible, but it allows me to stay with in the NH laws as a "pedal assist" motor driven cycle.