How to build a massive single-family house most cheaply?

Town & Country Flair 152. Move the wall and door in the living room a bit, this way you get a 15m² children's room on the ground floor. Upstairs there are 2x15m² children's rooms and optionally a large bedroom with a dressing room or a small bedroom plus a small dressing room and an office.

The living room is only 23 or 24m², but the kitchen is nicely large with 17m². A dining table fits in there.

Currently costs around 330,000 EUR including underfloor heating, air-water heat pump, manual shutters.
2,200 EUR/m². A bit of upgrading (RC2 windows should be standard)
Floors, walls, interior doors depending on skill, kitchen as DIY work, then you can get under 400,000 EUR.

I still don't understand how people get to 3,000-3,500 EUR/m².

What do you understand by limited budget?

The key to affordable building is a simple building shape and a slightly smaller house. With 3 children, you can also live on 130sqm. At 3000-3500€/sqm, the smaller size should save you a large chunk of money

However, the smaller size does not correlate directly with the price per sqm. In other words, 30sqm less does not equal 30x3500 EUR saved. The main costs for heating, sanitation, roof, and electrical work still remain high. For example, in our case, according to the general contractor’s calculation, 20sqm more living space only caused about 15,000 euros in additional costs. Let's also say about 5,000 more costs for floor and wall coverings.
You can save much better in other areas.

The most money can be saved by not withdrawing. Sanitary ceramics do not have to be from Villeroy & Boch, it does not have to be parquet everywhere, and tiles do not have to cost 60 EUR/m². You do not necessarily need a fireplace, no 25 network sockets, no 150 power outlets, etc.

I still don’t understand how you arrive at 3-3,500 EUR/m².

Let it be 2800€ for my sake if you try to build cheaply. Although prices here in the south are somewhat higher than where you are. Also, photovoltaic is now mandatory, which hits the "cheap house" price quite hard.

But the smaller size does not correspond with the price per sqm. In other words, 30 sqm less does not mean saving 30 x 3500 EUR. The main costs for heating, sanitary, roof, electrical still remain at a high level. For example, in our calculation with the general contractor, 20 sqm more living space only caused an additional cost of around 15,000 euros. Let’s say there are another 5,000 euros extra for floor and wall coverings.
You can save much better in other areas.

Yes, costs do not necessarily scale linearly. Nevertheless, you can save a good chunk of money with 30 sqm less. Your example is certainly on the lower end, most providers charge significantly more than a thousand euros per square meter for expansions.

An interesting question would be the TE’s budget for the house, incidental construction costs, and outdoor facilities.

The approval authority does not require a site manager. I also did not hire the architect for that back then, he then wrote to the district office and they quickly carried out a building inspection.