Is a house for a total volume of 400k still possible at all?

In my opinion, this is not a zero-sum calculation.

In my estimate, I also took into account the compensation for the area lost due to basement replacement rooms. With expensive building land, a basement eventually pays off. If not in numbers, at least intuitively.

Although I admit that a basement is usually oversized for what it is supposed to do.
But with 360 sqm, building upwards is basically the only option if you don't completely disregard having a garden.

Otherwise, I fully agree with your post.

puh that is really frightening that nowadays you can't even get a "small" house with a basement for 400k.

Would an attic that you only convert at a later time be an alternative to the basement? Or maybe a workshop behind the carport/garage/parking space? Or perhaps a small garden shed?
Would you like to let us know how urgently and for what purpose you need the basement?
We are building without a basement.

Insanity to spend so much money on such a tiny cabin without a basement and garage. For me, that would be the point to say, I'll leave it and rather rent something proper.

I can only fully agree with KingJulian on that. At some point, it stops being fun when you have to give up so much.

I didn’t write for no reason that the 400k€ all in probably won’t be enough even without a basement. At least the advantage of the OP is that he apparently can do more but doesn’t want to.
Just like the floor plan design, the budget planning is also a process. First, the general contractors lure you in with offer prices, after signing you realize that not everything is included. During construction, it gets even more expensive and in the end, you realize that the general contractor also misled you in the budget planning for the outdoor facilities (usually they throw around 10k€ in that regard). Meaning, towards the end, there’s also the sobering realization there.

...as written, everyone has to go through that.

I see it as almost impossible to fit all of that into a 125sqm house without a basement. It should be mentioned that we are a household of three.

On that point, I would trust the forum (not me) if I were you. I am sure the forum members here can manage it.

A colleague was persuaded not to build a basement. Now he regrets it. The double garage is now a substitute basement and both cars are outside.

A needs analysis, as suggested by ypg, is especially important with regard to a basement. I feel sorry for your colleague, but he didn't seem very convinced by the basement concept anyway, otherwise he wouldn't have given it up. Either I need a basement and know exactly what I am spending so much money on, or I don't need it and just "want" it. If two above-ground rooms (in his case garages) are enough, I don't necessarily need a basement, in my opinion. Above-ground rooms, even if they are just repurposed garages, I would always prefer to a basement (not a walk-out basement).

I have often wished for a basement or at least that the garage had been built at the same time.

Maybe a silly question, but purely out of self-interest, because we are considering this: Would a garden shed (either one that is removed later or one that remains) be an alternative?