Use L-stones for slope stabilization.

The stones are 60cm high??? Ok, they are probably even without reinforcement, right??? That also explains the price.

The stones are 60cm high??? Ok, they probably don't even have reinforcement, right??? That also explains the price.

Yes, the 60cm ones are still without reinforcement. Probably the 80cm ones too. The big ones from 100cm up (fortunately the seller had to pay for those on one side of the property) are reinforced, but here they don't cost much more than 100€ (if you can reasonably get to the place where they are to be installed).

We have stones from 2m to 1.60m.

We installed 1.50 meter stones in double rows – since a height of 3 meters needed to be secured, and with the neighbors' approval, a maximum of 2.00 meters would have been possible. So, one L-stone of 1.50 meters was placed and the second row was stacked behind it at a distance of 0.50 meters.
Regarding the topic of doing it yourself, an old joke comes to mind:
The man goes up to the attic. His dear wife says to him: "Since you’re already up there, bring the piano down with you." He replies: "And what am I supposed to carry in the other hand?"
(This one is so old, you have to be careful not to trip over the beard.) But it fits nicely here.
back to topic: You can also possibly order directly from the concrete plant (e.g., Kann-Beton).

We were offered the 80s completely with antifreeze and reinforcement for 182 euros per meter.

We did it ourselves and installed stylish hollow bricks. It was much cheaper & without heavy equipment