Thank you for the answers. Those are huge differences. The problem is probably the water protection area, since you are not allowed to use antifreeze here and therefore have to drill deeper. At least, that's how I understand it now. And the 14k are net prices, 19% VAT will be added.
We have enough space for the heat pump in the basement. That will not be the problem. Here is the offer from the drilling company:


If I then add the heat pump, I'm quickly close to 40k for the whole thing, right? On the other hand, the general contractor wanted about 37k for the complete heating system with an air-to-water heat pump. That could almost work out with the BAFA subsidy.
I think I will ask other drilling companies for offers again. Then I would have a real comparison.
