The same tiles throughout the entire ground floor and in the bathroom - also the same in the basement?

Härddie is the Jääscher

Another quote from somewhere and I don’t know it. Please explain, oh great master of word acrobatics :-)

oh great master of word acrobatics

... would be a label I would have to reject - I will not be able to hold a candle to Willy Astor anytime soon.

Another quote from somewhere and I don’t know it.

It originally refers to the fox above the shoulder from the Hannelörsche: "Hello, I am Hermann," Rodgau Monotones 1985.

In the basement, I would take dark gray (not anthracite) tiles from the very bottom of the shelf and definitely spend no more than 10 EUR/m² on them. But that's just me.

That saves less than you think. The expensive part of tiles is the labor. If you pay 110 EUR/m², maybe 30 EUR/m² of that is the material cost for the tiles. The rest is labor and small stuff like tile adhesive, grout, silicone, edge trims, etc. If you now take tiles costing 10 EUR/m², you save 20 EUR/m² because the rest stays the same. Besides that, I’d rather not see a tile with a material price of 10 EUR/m². It cost 5 EUR two years ago; tile prices have skyrocketed. You can really only save on tiles if you do it yourself. Like with everything, actually, when it comes to floors and walls. The labor is expensive here, not the material. Then better take something decent in the basement too, something you don’t have to chip out again in 5 years because the cheap stuff annoys you.

Yes for tiles, no for other floors. We would have been paid just under €20/sqm for the floors, after deducting the materials. Glued installation by the way.

In most construction companies, the floor for the entire house is not included in the standard. It may have been different for you, but you also see 3,500 EUR/m² as the minimum price for standard equipment... ask yourself why...

As already said. You can save a lot of money on floors and walls because doing it yourself is not rocket science and serious mistakes hardly ever happen. I mean mistakes that would ruin the house in the long run.

In the basement, where it is not that important anyway, you can safely try your hand at being a tiler yourself. The tiler charges 50-70 EUR/m² just for the work... without the tiles and small materials.

It rarely stays at 30 EUR though. In my opinion, the OP rather saves 30-40 EUR per m2 here. With an area of, say, 60m², that’s 1800-2400 EUR. If that doesn’t bother you. Yes, whatever, you can also put designer tiles in the basement. By the way, I have 10 EUR tiles in the utility room. At least in the hallway, those would have been the better solution everywhere, in hindsight.