KfW55 with a general contractor, size approx. 120 sqm on 2 floors. The price includes underfloor heating with a laying distance of 15 cm, in the bathroom 10 cm.
Then it is a "standard" planning without proper fundamental planning. Higher supply temperature and/or intended for fossil energy sources (since you are getting a heat pump, the former). You will not achieve 30/26 temperatures with it, so it will be less effective.
According to your estimation, what additional costs per sqm should be expected if the laying distance is reduced from 15 cm to 10 cm.
That is about 3 meters of pipe more per sqm. For 120 sqm, rounded up, about 400 m. A 500 m roll costs between 400 and 500€. Installation might take 2-3 hours longer. The heating circuit distributor will be bigger, the number of ERR probably remains the same. So real additional expense in € still under 1,000€. But you should also get a proper heating planning with calculation of the room-by-room heat load (considering the temperature you want - which you probably have not specified yet). HOWEVER, you will have to pay the price your general contractor sets for you. And he will certainly calculate very well for himself...