How cheap can parquet be?

Yes, but for 20 sqm...

If not much has to be pieced together there, it doesn't make a big difference.

Calculate 50/sqm installed net, so plus tax. Material installed. 28 for the stuff, 22 for the laying. As a student, I worked in a laying crew, got good hourly wages in 1980. It certainly won't be over 12 hours. The gluing goes quickly. You just pay a flat rate also for travel times and downtime of the people.

28 euros per sqm for parquet? Isn't that extremely low for the material?

Didn't you mention 28 further up? Or did I misread?

We laid parquet flooring in the bedroom and dressing room for ~27€/sqm. Knotty rustic oak, brushed and oiled. I'm also glad I didn't choose laminate or vinyl, it's just something different. The gluing itself is not a big deal, I had never done it before. Only the subfloor really needs to be prepared thoroughly. I neglected that a bit and ended up with a hollow spot. Fortunately, the bed is standing on it.