Realistic offer for a prefabricated house?

The house is a shell house, you still have to add the costs for the finished condition.

What else would need to be done besides: additionally the finishing work (walls, floors, bathrooms, interior doors)

The text sounds like Massa Haus. Modern Style 134?

YES, it is about the Massa Haus. Modern Style 134.

what else would need to be done apart from: Additionally, the finishing work (walls, floors, bathrooms, interior doors)

YES, it is the Massa House. Modern Style 134.

then don't expect any goodwill + high additional costs

are there any reports? can you link them to me? that's why I'm asking.... because I have no idea and before I act, I'd rather ask...

Don't forget the real estate transfer tax on 200K.
Additional construction costs with 22K are too low!
Kitchen missing, lamps missing, curtains missing
Interior finishing minimum 30K calculate (basic equipment): bathroom equipment 5K, tiles including self-installation 30€/sqm, flooring including self-laying 15€/sqm, wall filling, sanding, smooth plaster (all DIY) 10€/sqm, door including installation 200-250€ minimum, adapted pleated blind 100€ per window

On top come the earthworks Estrich Who tiles the bathrooms? patterning Interior plaster or filling and sanding (don't forget the ceilings)

In particular, there is a dedicated forum for the manufacturer. You will find a lot there