when you are doing your apples to apples comparison, remember to add in a few extras on the car side.
A car rented in Switzerland will already have a Swiss Vignette, but it won't the Austrian one. Once you know your number plate you can get an electronic Austrian Vignette so you don't have to mess with getting the sticker in exactly the right place on the windscreen.
It almost certainly won't have a German Umweltplakette which means you can't drive where one is required. Urban Munich and Stuttgart are out. That's OK because you can park in the outer suburbs, probably stay out there, and take train or tram in.
Most times you park you will have to pay - at hotels, atracrations, car parks. It can add up quickly. Plan on at least 15€ a day to park in Salzburg, for example.
Speeding tickets are expensive and controlled by automatic cameras. You need to know the national speed limits, the ones which don't appear on signs but you know by circumstances, and the three countries you are visiting each have different ones. Understand that passing the sign announcing the name of a town, village or city means that the boundary has been crossed for the lowest speed, usually 50 kph. It starts at the sign, not when the car slows down by you taking your foot off the gas. There are often speed cameras just after the sign. You may not recognise it as a camera, thinking it is a simple pillar.
Insurance can double the price of a rental - be sure that when you compare you have included all the insurances you will buy, especially the ones you will be sold at the counter.
Become familiar with the German word "Stau". It wil be on signs and you will be in them. Part of life, I'm afraid.
It sounds like a lot of learning, and it is. I have to drive (my English right hand drive car) every year because of my wife's disabilities, and it is all second nature to me, You have a bit of a learning curve - but you'll get there.