Hello,
it is indeed correct that you cannot generalize the prices for a central vacuum system. However, what you can do is give a rough estimate and a recommendation.
A good device costs between 900 and 1000 euros. With installation and piping system, a system for a [REFH] should not cost more than 2000 euros. I recommend devices and piping systems from the company Disan. Disan makes very good and very reliable devices. We have had a system in our house for 15 years and so far only had to replace the filter once. The system runs perfectly and extremely reliably. Also, some of my relatives have installed central vacuum cleaners in their houses on our recommendation. With some DIY skills, you can even do it all yourself. We had our system installed, but the central vacuum cleaners of my relatives were all installed by themselves.
Our system was installed back then by the company SSE-Zentralstaubsauger. However, the company is located in the middle of Germany, in Kassel, and will hardly install systems in Switzerland.
So that is my recommendation. I hope you will find what you are looking for.
Best regards