Construction costs - Are we that far off?

Was that a prefabricated house or why did all the walls have to be sanded?

No, massive. Prepared with interior plaster in Q2. Since we wanted a completely smooth appearance, the walls and ceilings had to be sanded afterwards to achieve a Q3 finish. Otherwise, even the smallest irregularities would have been visible through the fleece.

Ok, then that is also somewhat more elaborate... If I were to wallpaper on normally plastered ground myself otherwise, that would be very ambitious...

Painting work €15000 ???

In total, the OP wants to create 240 sqm of floor area, roughly multiplied by 4 results in just about ≈ €15.50/sqm of wall surface; so comparatively little. 'Masipulami' has very nicely described which work steps are required.

Of course, you can also go ahead and remove the "noses" in the plaster, spray primer on the wall and then stick a thick, cheap wallpaper; alternatively process woodchip wallpaper using spray technique.

Rhenish greetings

Ok, then that is also somewhat more elaborate... If I were to wallpaper on normally plastered surfaces myself otherwise, that would be very ambitious...

It always depends on what is included in the package. With us, the painters were in the house for a good 2 weeks.

If we had wallpapered the walls with woodchip wallpaper, the substrate would not have had to be prepared so elaborately and it would certainly have been cheaper.

As said, the arrangement is then understandable. For us, the plaster was very smooth (or had already been sanded, which I don't know, although painting work was not included) and after wallpapering it looks good to us. Whether wallpaper now costs 5 or 50.- per roll is actually irrelevant to us, it has to be pleasing.