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

Sorry, but for a floor that will be there for 30, 40 years, 2,000 EUR won't ruin anyone. There are about 2,500 other things where you should rather save, especially since he wants the same tiles for optical reasons as in the rest of the house.

As I said, you don't save that much because no one takes 10 EUR tiles. Not even in the basement...

He can also save there additionally. Then he can spend more money on the 50 really important things, for example underfloor heating installation spacing. Concrete ceiling also to the roof, basement in the thermal envelope, walk-in shower with sloped screed instead of a bathtub. Floor drain in the utility room. Floor area. So the things that you really never go back to. Besides, I wrote how I would do it and not a universally valid law. And I wrote that if he has the money, he can do it that way. But you always have to have the last word again.

Huh? He is choosing tiles, which means all the other stuff, like underfloor heating, upper floor slab, etc., has been planned and ordered, if not even already built?

Sometimes it really gets weird here... when you say nobody needs SmartHome, it gets heated, Stone Age blah blah, and when you say you don’t save that much money with cheap tiles, also. But I take it sportingly ;)

It’s also the question whether the tiler even installs cheap tiles at a material price of 5 EUR.

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

Your statement was that installation is more expensive than the material. I disproved that with a counterexample. Whether it's included with the general contractor or you hire the floor installer directly makes just as little difference as the usual price for conventional laundry detergent. And if you value your own work at €0, that applies even more ;) Floors are often not included because potential customers like to imagine it otherwise. Laminate flooring is available for €20, so the floor only costs €2,000 if you do it yourself... ;) And yes, you can do it yourself. But I wouldn’t have managed that so quickly, especially not when also preparing for the move. You had that done, so financially it balances out. At some point, it’s also penny-wise pound-foolish to install a relatively expensive and durable floor crookedly and unevenly yourself.

if not even already built?

True. The screed is laid and drying (unfortunately poorly in this damp damn weather!)

The question is also whether the tiler even installs cheap tiles for 5 EUR material cost.

In the meantime, here is a price example / offer that I have received. How do you assess it?

We have planned tiles throughout the entire ground floor of our new build, similar to those in the attached photo. They are called Kermos Stoneline naturbeige 30x60. We also planned to use them as wall tiles in the bathroom. Now we are considering having them laid everywhere in the basement as well. Would that be "too much of a good thing"? I would be interested in your opinions and also pictures here.

We did it this way. On the ground floor entrance area, almost the same tiles as you have, as far as the ground floor guest toilet and wardrobe. The same tiles were used on the upper floor in the parents’ and children’s bathrooms. We were always confirmed a very uniform, beautiful look/concept.