Offer comparison and liquidity planning for new construction, any experiences?

I don't understand: the choice of the plot apparently hasn't been finalized yet, so where does a concrete development plan come from and why does it only allow angled houses? By the way, the cellar question can only be answered affirmatively or negatively with regard to the specific plot. Whether you need a cellar or can even omit it is not a matter of willingness or price. Only when the plot says "not necessary" can you leave it out or substitute the "cellar space" above ground. Otherwise, it's a naive calculation.

The development area we are applying for is already completely fixed. We have all the documents including the development plan and we know the slope etc. and know that no cellar is necessary.

You mean the houses that the boomers usually built themselves alongside their dead-end jobs from 6 a.m. and small children’s legs, and raised only with their own efforts? Is your sentence now irony or just plain disrespectful?

This is simply called demography and you are mixing your personal feelings with reality here. Of course, the case will occur, but that doesn't help us much now, because we need something now.

Now back to the actual questions: As I read the previous answers, I am calculating everything correctly and it is simply that expensive. Then thank you for the answers, I don't need anything more to continue.

"It" is not just expensive for no reason. You can decide what you want to base your demands on. The large group of high earners often like to claim about themselves that they don't have big demands. 170 sqm is already quite generous, 2x office rooms too. Nationwide, people have managed with what they had. It can be done differently. Carport, photovoltaic system, electric shutters, and so on. These are definitely sophisticated demands. But it seems normal to you. That’s why I just want to briefly say that there is still room to go lower if you want to build yourself.

When you die, the second office and the home battery won’t be what brought you satisfaction in life.

Almost everyone here lives in houses from the 1930s, with surface-mounted cables, visible radiators, office stuff on the corner of the dining table, and children's rooms of 10-12 sqm. Without any problems. So that works very well too. Even better than in a new building, I would say. You just have to dare. A terraced house is also great. After that, you can always keep looking if it doesn’t meet your demands.

"It" is not simply expensive without reason. You can decide where to direct your demands. The large group of high earners likes to claim to themselves that they don't have big demands.
170 sqm is already quite generous, 2 x office as well. Nationwide, people have made do with what they had. It can be done differently. Carport, photovoltaic, electric shutters and so on and so forth..

That is clear to us as well and we are also continuously lowering our demands, and afterwards it will just be the townhouse or smaller area etc.
My question would still be what specific saving possibilities there would be in such a case. I understood that we will also inquire with the "cheaper" providers and thus things like carport and storage battery will also drop. For example, I do not want to miss the second office, as it will simultaneously serve as storage (since no garage, attic, or basement) and guest room.

But we only inquired with the well-rated companies:

What does well-rated even mean? A good legal department that makes every critical comment disappear? You always have to assume: the bigger the company, the more you pay for all the bells and whistles around it. Salespeople cost money, show homes cost money, catalogs, websites, etc. etc. All things that might be nice, but you gain nothing from them (except that you lose a lot of money). Architect is fine and all, but with the building sum and with KfW, the entire program then heads into six figures.

The equipment wishes are, well, not exactly extraordinary. 50 euros for floor coverings, that's normal nowadays. Electric shutters too. The real money is earned on the change orders.

Pitched roof, green roof, yeah, you have to make a cherry out of it, something that the suit-wearers from the show homes usually can't do.

Photovoltaics with storage: You want KfW, so there's no question. 300 is like 297, so 40+ QNG.

Saving costs: the sliding window in the living room, that's almost as expensive as the rest of the windows on the ground floor combined.

Oak staircase: well, you can get a German one for 20 grand, a Pole will do for 10.

I'd rather place the thing at 500, including architect etc.