Construction costs are currently skyrocketing

That is basically basement sqm price. Or well-developed garage sqm price.

We live similarly ([Speckgürtel Münster]) and paid 350k in 2022 for 156m² of living space + 40m² garage, turnkey. Not included were - floor coverings on the 1st floor - painting work - outdoor facilities - photovoltaics So it is comparable, only that we were lucky enough to still get the pre-war prices.

that is 2200€/sqm turnkey. These are prices from about 10 to 15 years ago...hard for me to understand right now

The term turnkey is also extremely vague. As mentioned, quite a few items were not included. But we also did a lot of work ourselves. Many general contractors included extras that we saved on, e.g. the ventilation system (please no discussion). That would have been 11k more for us. No finished attic with huge roof windows. Or kitchen. It just wasn’t the Berbel hood for €2000. Or the oven has no pyrolysis. That would have been nice, but also "just" €400 more. The equipment makes a big difference.

Absolutely, the materiality and equipment determine the price.

Or kitchen. In that case, it just didn't become the Berbel hood for 2000€. Or the oven doesn't have pyrolysis. That would have been nice, but also just "quickly" 400€ more.

Kitchen has absolutely nothing to do with construction costs. Or do you then also include the new car? Or the riding lawn mower?