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

Good morning, thank you for the feedback. Actually, the outdoor area is a big question mark for us. Maybe I can ask the civil engineer about some costs today. I have looked at the construction and performance description and (but I am a layman) found nothing unusual. I think that we will definitely have to upgrade 5000-10000 for the electrical and staircase. And quite a bit more for plumbing, interior doors, and floors. Are there any other aspects I should take a look at?

Good morning, thanks for the feedback. Actually, the outdoor area is a big question mark for us. Maybe I can ask the civil engineer about some costs today. I have looked at the construction and service description and (but I am a layman) found nothing suspicious. I think we will definitely have to spend 5000-10000 on the electricity and stairs. And quite a bit on plumbing, interior doors, and floors. Are there any other aspects I should look at?

I can only give you the tip: don’t ask the civil engineer. If he doesn’t also do landscaping, he has no clue about prices. That means, ask a garden landscaper if you are going to have the outdoor area done/have to have it done. I can tell you, my neighbor spent almost €80k. We are also at about €70k without a carport. Everyone said €20k would be enough..

Look here:
https://www.hausbau-forum.de/threads/liste-der-anfallenden-baunebenkosten-bauseits-teurer.9737/
I myself posted the upgrades there. Although the prices are no longer accurate, the terms like bathtub 180x80, podium, SAT, outdoor faucet, outdoor podium, mirror, and sockets should encourage you to a) check your construction service description and b) consider whether you would/should upgrade it yourself.

Ok thanks, I'll take a look at it. Excuse me, 80k for the outdoor area? Then I might as well forget about the construction project.

The outdoor area is the absolute killer. You have to divide it into 2 steps. First step: all the fixtures, paving, lawn, and edges. Normally, you’re already easily out 50 grand. Then in the second step: planting, design, and the "beauty" of the garden with everything that goes with it. That’ll set you back another easy 20 grand. So a garden costs about 70k to 100k when it’s finished. If you add a pool or such playthings, you’re quickly well beyond that.

So by now we also have all the offers for the outdoor facilities together and if we were to award everything, we would also end up at 75k. Since we want to do a lot ourselves, we hope that we can manage it significantly cheaper, but as an exploration of the "worst case," the offers have already helped us a lot. Friends of ours on the hillside paid over 100k for the outdoor facilities and our future neighbors also paid a total of 80k. So in our area, you probably unfortunately have to reckon with these amounts.

However, for us the basement and the house are also significantly more expensive than for you (with an average standard), so there apparently seem to be very large regional differences. We have almost paid for the shell construction what your whole house apparently should cost.

For us, it was like this with the prefabricated house suppliers that we were given a price for our project in the show house exhibition (roughly based on square meters). When we then planned more concretely, a fireplace was added, windows in aluminum and RC2, controlled residential ventilation, electric shutters, different stairs and a few other "small things," and then the price was suddenly 100k higher. But if these major items are already included, then hopefully your 30k is a reasonable buffer.