Planning: Demolish an 80m² old building, erect a wooden house

In short, you get a shell kit for a house to be finished.
From the necessary connections including wiring and technology (electricity, water, heating, ventilation), the prior building permit, the interior finishing (floors/walls/bathrooms) up to the still required construction of the foundation or floor slab, everything still needs to be done.

Conclusion: The house will ultimately be just as expensive or cheap as any other house. Although I don't want to speak ill of the houses. As a bank, however, you would not get a loan from us for the house, as it is rather classified as a holiday home.

Where can I get such a house, can someone link me such a house for that price?

That would then also be an option.

Oh yes. You have calculated with your small costs about €2,000/sqm of living space (which will probably not be enough). Normal low-cost house builders like Town & Country also start at these prices.