House construction 130 sqm turnkey

Thank you for the detailed answer. And what would you consider a realistic price for 140 sqm with a basement?

Maybe you should first answer the questions yourself if you want to get realistic answers

allegedly everything is included there, including all ancillary building costs and the basement.

Allegedly...

They reportedly told the developer a maximum budget of about 300,000 and that they want a move-in ready house with a basement. And he then said he could manage that and said the house would be about 140 sqm plus basement... Next week he would present a finished offer..

Who or what is this about? About hypothetical questions or concrete construction projects?

Here is an overview from the developer's homepage. Are there any essential things missing here?

... right at the top of this forum section is the pinned thread . Someone took the trouble to list all the costs that were incurred during construction as an example. And there are a lot of costs included that I don’t see on your list, e.g. connection fees, charges, etc. Just have a look at it.

Here is an overview from the developer's homepage. Are there still essential things missing here?

At first glance, it reads like a car order: Vehicle with - four wheels - fuel tank - seats - engine - heater - windows etc. Is the car now good and complete? Neither quantities nor qualities are mentioned (except that it is an energy saving ordinance house). And there are no items that the builder has to take over – clever.

Yes, of course, all additional costs except for earthexcavation are missing.
With earthworks, you also don't know exactly what is included.
Up to what depth? Is transport included?

Otherwise, for example, with us
- Connection fees for municipal utilities 11.5k
- Wastewater 4k
- Construction electricity 2k
- Construction water
- Building permit
- Surveying 3k
- Energy consultant?
- Building inspector?
- Insurance 1k
- Notary fees, land register for mortgage

Otherwise, I would never sign this based on the information given.
Where does it say, for example, how many power outlets are included?
What do you do if 2 per room are included and every additional one costs 200€?
Painting work is definitely not included. Costs also 10k without own contribution.

Should everything now be purchased complete including the plot from the developer, or is it about a general contractor who is supposed to build on the self-purchased plot?

This dithering over details is also unpleasant. First you ask for the cheapest house, then at some point the requirement comes that a basement is desired. A basement is always expensive and never included in the offers.

I'll ask the other way around: How much income and equity do you have?