By much you mean the weight of the motor, which actually is not the main weight of the bike. Batteries tend to be removable or easy to gut.
The frames may sometimes be a bit more heavy duty, but usually aren't.
The motor is noticeable on a super light carbon bike but not really on aluminum and definitely not on steel frame.
5-10 times more expensive is also a lie, at most I've seen 2x over comparable non-electric. (Though instead it should be a flat price increase.)
Thing is, many ebikes are in premium segment. But there are many cheap ones as well.