Good morning keroysn,
I don't want to go further into the above-mentioned calculation, but calculated with the house price on 127m², I think (I am still in the preliminary planning) it won't add up. You should use 1600-1800€ per m² as a guideline. Without cellar, without garden, and without garage.
These are the values I have been able to find out so far and which have also been noted here in the forum.
Regards Andi