Certainly, you can't illustrate it exactly like that. But I think what the OP meant were the offers from the house companies.
These are basically calculated without a basement and additional costs. The attic is also not included in that calculation.
If I now calculate 1,600.00 EUR, you are already in the upper price range.
We also had many discussions with house companies and a man (company Fingerhaus), with whom I liked to build (he was very nice and sympathetic and tried everything) said:
"Definitely not 1,200.00 EUR. Because something can't be right, or services are missing, etc..."
This statement came from an honest mouth and not from a man who wants to sell his houses.
We are now building solid and after tough negotiations are at 1,300.00 EUR / m² living area with everything included, ready to paint.
With RENSCH - House (timber frame construction) we really liked a house, but Rensch-Haus was at 1,560.00 EUR / m² living area, far above our budget.
Best regards Florian