Perfect. Thanks for the assessment. With your details, I come to about 87,000 EUR. Can you tell me again what would be added if the basement were built as a "Weiße Wanne"? The plot is on a slope (about 10%). To estimate the worst case, I would include the "Weiße Wanne".
Provided you don't want/have to do in-situ concrete (which is generally noticeably more expensive than precast parts) and as long as you don't have any special static challenges, "Weiße Wanne" should be quite possible. However, as soon as it comes to areas with waterproof or flood-proof windows, light shafts, and possibly lifting stations, additional costs will arise. It depends on how your slope... goes.
In any case, don't calculate too tightly - maybe you have to pour concrete in winter, bam, a 5 to 10% winter surcharge. Or your street has to be closed due to delivery by truck crane and unfortunately is a district road, bam, another 1,000 to 2,000 € gone. And it goes on like this - so especially if you don't want to hire a general contractor with a fixed price, better to calculate generously.
With a 10% slope, you will probably build a basement, meaning somewhere open. Exterior plaster matters there, and you may have to provide regular windows and/or front doors - which will make it correspondingly more expensive.
Forgot to mention:
- approx. 90 sqm usable area covered with screed
- of the 90 sqm, about 40 sqm with underfloor heating (directly next to the boiler room) - no floor covering
In "Kfw40", it is rather pointless not to heat (large) partial areas. Possibly not even allowed (if certain limits have to be met due to subsidies).
Consider rather providing concrete core activation (or "Swedish slab") - with appropriate design, planning, and execution, you can save the underfloor heating, additional floor insulation, and screed in the basement, and also achieve noticeable efficiency improvements for your heating. Especially if cooling is planned.