Construction / Extension of Single-family House: Assessment of Construction Costs + Construction Description

Hello everyone,

we are planning to extend our single-family house. The building permit is available, and we also have an offer from a general contractor now. Location: Bavaria (Ingolstadt).

You would help us a lot with a

[*]assessment of whether the costs (turnkey) are realistic or too high, and
[*]info on whether the construction description shows any significant defects.

Existing building:

[*]Year of construction 2000
[*]130m² living space (ground floor + 1st floor)
[*]610m² plot
[*]solid construction with 36 cm bricks
[*]gable roof, garage built directly on the side of the house, built-in balcony, basement

Extension (plans attached):

[*]81m² living space, also solid 36 cm bricks, without basement

[*]house/roof extension by approx. 5m, with an additional cuboid pushed in sideways over ground floor + 1st floor
[*]in the "cuboid" on the ground floor + 1st floor each a room of approx. 32m²

[*]an additional room on the 1st floor in the extended new building (18m² with sloping roof)
[*]below an open terrace on the ground floor
[*]plastic windows/doors, 2 tilt-and-slide doors on the ground floor each 3m wide
[*]standard equipment (vinyl floors, CPL doors)
[*]additionally 5 skylights approx. 1.0 x 1.5m to illuminate the existing rooms, which would partly have no windows otherwise
[*]additional work is the demolition of the built-in balcony (probably needs to be removed for the new ceiling), as well as the flanging of the extension to the existing garage and a new exterior door in the old building.

Cost offer: around €240,000.
Construction description attached.

Thanks for your help!!!

That is very difficult to answer. At first glance, it seems relatively expensive; the rule of thumb of 2000€/m2 is clearly exceeded. But: small areas cost disproportionately much; there are apparently still demolition works (balcony); the whole thing must then fit with the existing building.
Moreover, in Bavaria (already high construction costs).
The problem will be to find anyone at all who does it. Therefore, the amount can indeed be correct, although from my point of view it is really at the upper limit of what is still acceptable.

I am curious about the further statements.