Thank you for your answers and the prices you mentioned. After discussions with other builders, they also gave me similar values. I would not have expected front doors to be so expensive. In the meantime, we had an on-site appointment with the fitter and the manufacturer (dth Tiemann) to clarify our questions.
As a result, I have to correct my initial post: We did not choose a simple version with the most expensive door but rather a quite elaborate one with 2 different types of glazing, stainless steel decorative bars, milled lines, a designer handle, and made from fiberglass-reinforced plastic (GFK). Not everything was visible in the catalog, and we first had to have this explained to us. The price is not gross but net. So, this door with automatic locking costs over €5,000, *gulp*.
The extra charge compared to aluminum would only have been €250 net, but we decided against it. The two contacts had more contra than pro arguments for aluminum, and there are very different opinions on the internet. It seems to be somewhat a matter of belief.
We did not look further into wooden doors. Presumably, the price and maintenance effort would be higher.
As a cheaper plastic alternative, we had another series (Porta smart instead of Rodenberg Premium) from the manufacturer priced for us.
There, the gross price would be €3,139.00 including automatic lock.
After successful price negotiations, we decided today on our favorite.
I hope the additional cost is truly justified and that the door will serve well for the next two decades.
One more tip for all other builders: If possible, also ask for catalogs with MSRP prices. We have now received five catalogs, but only the last one contains prices. So, we had no choice but to choose according to our taste and then wait for the prices. Otherwise, some doors would have been eliminated earlier, and you would have the option to make your selection directly based on price.