Coincidentally, the same as I used for my eclipse picture.

They're not rare in Eastern and Central Europe, and cost about 200...300 euros (more if the kit is complete or the lens has been well preserved, because some of them are 45 years old now).

Of course they are inconvenient (massive weight, no control over aperture), but this quickly stops mattering when a well-known camera brand charges several thousand for similar optics. :)

I've used mine to photograph a plane from 50 km distance. Of course I had to know in advance where the plane was, and weather had to be perfect, but it was doable. I could not catch a plane at 100 km, but I was able to snap a barely recognizable ISS from over 1200 km (I was in Estonia, ISS was passing from Poland to Ukraine). This I will try to re-attempt later, because the blob required lots of post-processing to start resembling a space station. :)