I have an IZIP Zuma electric bike with a lithium battery that has pedal assist and throttle. It can get about 12-19miles on a charge depending on if you are riding on flat or hilly streets. I ride it like a regular bike and when I come to a hill or get tired I switch on the pedal assist. I usually ride around the campground and on bike trails. They can go fast but I don't ride mine any faster than I rode my regular bike. When I complained about having to ride a stationary bike to help my knee, my Orthopedic Dr. suggested riding an electric bike with pedal assist instead. It is so much more fun than just sitting inside and pedaling. In addition riding a bike helps strengthen your core muscles and improves balance too.
Go to a bicycle shop that will allow you to try them out. The price varies by brand and battery kind and size.