Hanging attachment - planting stones or car tires?

That is an incredibly steep slope. What is "down there"? With us, the steep situation would not be possible because the embankment slope is limited to 30 degrees. How is it with you? Do you have all the freedoms there?

People have ideas. It slips off, at best only material damage follows. With tires, it basically works. However, you don't just stack them but anchor each tire in the backfill. That means you have to dig the slope 3-5m deep first and then build it up layer by layer. Your simplistic calculation of 1000€ + labor doesn't really support that. The tires are free, meaning it’s about approximately 5x5x10 = 250 sqm of soil reinforcement. That puts you between 10 and 20 thousand euros.

Under no circumstances would I just start, but also clarify whether it is even possible. If it is possible, it will be expensive :)

Have a look at Allan Block. With these, slope stabilization is permissible. Secured with gravel and geogrid. Angle of 87° possible.

Take a look at Allan Block. With these, slope protection is permissible. Secured with gravel and geogrid. Angle of 87° possible.

But that is quite far from cheap and simple. And at that height, still with drainage concrete or can you now gravel those things that high?

Without static calculations, it won't work. It will specify enough steel and concrete. Does the [B‘Plan] allow for terrain alteration? I would never use car tires. They contain toxic substances that must not enter the environment.