Which prefabricated house provider - prices, experiences?

Basement: €55,000

Additional construction costs: €30,000

From my own experience, one of the two amounts needs to be significantly increased. The basement price fits if it really only means the bare basement. Planning living rooms there could already become tight.
However, the earthworks for the basement are missing from the additional construction costs. The excavation can't be distributed anywhere there, and disposal really costs a lot. Excavation, backfilling, disposal... I quickly see an additional €20,000 disappearing there.

From my own experience, one of the two sums needs to be increased significantly. The cellar price fits if it really only means the bare cellar. Planning living spaces in it could become tight again.
But then the ancillary construction costs are missing the earthworks for the cellar. The excavation can't be distributed anywhere there and disposal really gets expensive. Excavation, backfilling, disposal... I see 20K quickly disappearing additionally.

Okay. What is your floor area? €70,000 for a cellar of a theoretical 120sqm house seems relatively high to me. It's a minor point, but I believe one could manage with €20-25K ancillary construction costs for the plot due to short utility connections (water/electricity/telecom) (excluding earthworks).
I don’t think €100,000 is due here for cellar and ancillary construction costs, unless you create a living cellar.

I am not talking about my cellar, which is (unfortunately) significantly more expensive. But we have juggled offers from 5 cellar providers, 3 civil engineering companies, and several potential landfills, so at least I know the local prices. We are also not in a high-price region. It was only meant as a hint that in the end, there may not be as much financial leeway as it seems.

Whether the basement now costs 55k or 70k doesn’t really matter. The added value on the property is simply absolutely priceless.

It is no longer indifferent when the missing 15T simply are not there and the Earth prevents further construction.

I see the added value the same way, but those are different things.

In the case of the TE, there would then be 25K€ left instead of 40K€. Therefore, it should still not be a problem.