The land prices here are around 1000 euros per square meter, so only 260,000 euros remain for the house and additional costs. We need about 120 square meters without a basement.
That is probably the point ... a maximum of 260,000 euros remain. And one should actually refer to
https://www.hausbau-forum.de/threads/liste-der-anfallenden-Baunebenkosten-bauseits-teurer.9737/
and
https://www.hausbau-forum.de/threads/warum-ein-Hausbau-fast-immer-teurer-kommt-als-kalkuliert.16237/
And then it has already been referred to
https://www.hausbau-forum.de/threads/Hausbauvertrag-kündigen-falsche-Beratung.31642/
This thread shows precisely that one should carefully question the offers according to the lists here in the forum BEFORE signing the contract and also get in WRITING things that the general contractor quickly dismisses. This is so that the budget of 260,000 can actually be adhered to.