Renovation of old buildings, what awaits us

We would basically invest the entire purchase price again in renovation costs.

... if everything goes smoothly ...

Yes, that's how it is. It will still be cheaper for you than a new build. In my opinion, the decisive factor is whether you are the type for a used property. A used property can often be inhabited immediately, it does not have to be completely up to date, you may partially like it unconventional and can make do with many things. From an energy perspective, it may also be the case that you waste a few extra hundred euros on consumption before you replace one or another window.

The quality of life lies in the mature structure, the garden, and individuality.

€10,000 for electrical work seems hefty to me too... What exactly needs to be done?

If you can do it yourself and are not planning something very elaborate or luxurious, that is ample; if you have it done, then it is probably realistic...

You are probably right, but it is not about new construction. I assume that in the affected old building, empty conduits are already present. This already eliminates a lot of work; only here and there will it be necessary (if the future residents consider it necessary) to install additional sockets or to relocate a light switch. The cables already in place will probably still be good; at least, I can’t think of anything that would cause the cables to deteriorate. The kitchen is probably an area that should be rewired or secured differently, for example by distributing work sockets across different RCDs and the like. Completely removing the old wiring and installing new is only reasonable in my opinion if porous cores/cable sheaths are involved or surface-mounted cables are installed. Otherwise, new electrical wiring makes less sense in my view. A new fuse box with RCD instead of a fuse should certainly not hit the budget that hard. All in all, most of the electrical system can presumably be retained, so I was a bit surprised by the price of €10,000. Many electricians, by the way, are not opposed to you doing the chasing, installing the empty conduits, and possibly pulling the cables yourself due to high workloads. You just have to coordinate that with the specialist.

You're probably right, but it's not about a new build. I assume that in the affected old building, empty conduits are already present. That eliminates quite a bit of work, only here and there will it be necessary (if the future residents consider it necessary) to add more sockets or occasionally move a light switch.
The already existing cables will probably still be good, at least I don't see what could be wrong with the cables now.
The kitchen is probably an area where you want/should wire or secure differently.
For example, distributing work sockets across different RCDs and the like.

Completely removing the old wiring and installing new is only meaningful for me if the cores/cable sheaths are porous or if surface-mounted cables are installed. Otherwise, new electrical installation makes less sense in my view.
A new fuse box with RCD instead of a fuse link should not hit the budget that much, anyway.
All in all, one will probably be able to keep most of the electrical system, and therefore the price of €10,000 surprised me a bit.

By the way, many electricians, due to high workload, are not opposed if you yourself chase the channels, install the empty conduits, and possibly also pull the wires. You just have to coordinate with the professional.

Uh, not in all houses, or hardly any, are empty conduits laid from the meter cabinet to the socket.
And even if they are, you first have to get cables through...
From a certain age, it already makes sense to do everything new.
And a fully equipped meter cabinet quickly costs over €1,000.
If you only need the material, you should definitely be able to stay well under €10k...

Naming prices per square meter is unreliable. After all, the scope of renovation varies greatly and is usually not comparable. Everyone also has different requirements. One just has to be aware of the higher costs, such as wastewater (easily five-figure), windows, [WDVS], roof, electrical work, etc...

The 1000.-€ probably refers to a complete renovation, which is likely about right when you compare the costs of interior finishing in new construction. In new construction it may be somewhat cheaper, but also simpler...