As with most, or at least MANY things it life...........it depends. You can spend around a grand on a pedal equipped, low powered "ebike" which has supplemental electric or small gas engine...
Motorbikes, in the United States, have a wide range in prices. They can be as little as $4,000 or as much as $18,000 and higher. Generally, the price of the bike depends on how big the motor is.
Most motorbikes fall in the 160kg to 220kg (350 - 480 lbs) range. Big bikes like cruisers and sport tourers are generally heavier than 220kg (480 lbs) and can weigh over 350kg (770 lbs)!