Find out the cost for the whole house design, then divide by square meters?
Some things on that house will be independent of the floor size - you'll still need the utility connections and a heating system, for example. The price of the ground may also be indepenent of the house size (sure, you'll need a larger piece of ground in order to build a larger building, but over here, you have to buy a whole parcel of ground, no matter the size of the house you put on, within the permitted limits). Also any auxiliray buildings (like a garage) will be independent of the building size.
The there are things like the exterior walls, which will not depend linearly on the floor size - or the roof construction. In the end, the only thing that will really depend on the floor area are the carpets (or other flooring) and roof tiles. And even there, youo can easily have a variation of a factor of 5 for different styles or quality.
Looking at your plan, it shows no room for any installations (heating, water, wasterwater, electricity, phone connections?) or storage (ok, there's that one small cubboard) - but it also doesn't show any access to a basement.