ᐅ Is the additional cost for masonry realistic?

Hello.

My wife and I have been in the planning phase with a builder for three months. Today, we received the first cost estimate including additional charges for some extra requests. In particular, I was quite surprised by the extra costs for a different type of masonry and would like to get your opinion on whether this is an exaggerated price or a realistic/typical surcharge.

We plan to build a single-family house with 155 sqm (1,670 sq ft), 1.5 stories with a pitched roof and a knee wall height of 1.25 m (4 ft). The builder’s standard according to the scope of work is aerated concrete (AAC) 36.5 cm (14 in) thick with a thermal conductivity (lambda) of 0.10. Here are the additional costs for other masonry types:

42.5 cm (17 in) aerated concrete with lambda 0.08 → €19,000

42.5 cm (17 in) Poroton T8 masonry → €25,000

42.5 cm (17 in) Poroton T7 masonry → €35,000

Thank you very much for your support

I just checked our quote and it says:
Stone 0.09, 42.5 cm (U-value ≤0.18 W/(m²K)) not completed. 9,090 €

The standard would have been:
Execution in 36.5 cm brick masonry, WLG 0.10

We are building 190 m² (2,045 sq ft) with a mono-pitched roof and knee wall 1.50 m (5 feet)