Calculation for basement (residential basement) realistic?

Possibly a lifting system if the shower and toilet are to be installed in the basement. By the way, the description does not read to me like that of a white tank.

You are totally right... I have reported it incorrectly... Can I still change that above?

It is as follows:

further measures for basement waterproofing against pressing water/white tank:

The exterior walls are constructed as reinforced concrete walls, which are connected to the reinforced concrete slab and to each other via special joint seals (sheets/profiles). The inner sides of the exterior walls would therefore not be plastered but only the joints of the precast wall elements would be sealed. The concrete quality of the floor slab and walls is waterproof (wu). Depending on the design water level, the basement light shafts are also connected watertight.

I find €88,500 quite steep. The area is not exactly huge either.
For the basement, we were often quoted an additional approx. 30,000 EUR. We also had a binding offer in that range, in which I actually couldn’t find anything missing, except earthworks. Of course, with [WU-Beton] and waterproof light wells.
It’s quite possible that additional costs would have come up (we ultimately built without a basement). But €88,500?

Earth 15-20K€, internal plaster 3, floor/screed with heating and covering 10, painting 3, stairs 3 (without covering), electrical 5 ...

Your 30K€ are basically the shell construction. That also only makes up part of the overall project for above-ground construction. Downwards plus earth, and the TE still wants a small bathroom downstairs ...

No, it was supposedly much more than just the shell. But whatever, I also consider 50-70 thousand euros realistic based on hearsay. I've never heard of 90 though.