E-bike are certainly the way of the world now aren't they.
I can't tell you about Vaduz rentals specifically - I've ridden through twice on different bike tours but never rented a bike there.
Bike price rentals in general in that area of Europe can vary from 120 euro per week to 250 euro per week depending on quality of bike and where you rent.
One bit of advice I would give you is find your rental bike, and then go to where the bike is to start your trip. The bike you want from the shop you want might not be in Vaduz. Even if you have to pick up the bike and take it on the train to some specific starting point do that instead of renting something that's not quite right from some place that you don't trust.
Are you actually bikepacking? In the US bikepacking means wilderness camping with the bicycle off paved roads. If so you're going to want to find the right type of sturdy bike, and if you don't own them you're going to want to rent proper bikepacking bags. Or are you cycle touring? Riding mostly on smoother roads and staying at mostly established campgrounds and hotels/hostels/warmshowers/etc? If the second then don't worry too much about which bike.
Have a great trip - it's a beautiful area for a bike ride!