$3 per gallon gasoline vs electric charge 5 cents.
Electric bikes typically travel at speeds of 10 to 20+ miles per hour and go up to 12-20 miles charge. Charging your electric bike for four to six hours uses 5 cents worth of electricity from common 110 wall outlets. The electric bike power can give you a break from pedaling or supply more power when you're going up hill.

http://www.bicycles-electric-bikes.com/bike_to_work.htm