Beyerdynamic cans for ~120 €: replaceable padding, replaceable headband, replaceable cord, replaceable transducers. Only the last two need tools.

Which model? I'm torn between getting the Sennheiser PXC 550-II or Beyerdynamic Lagoon ANC.

I have the DT 770 Pro, which I'm not sure they still make anymore, and it has been a ten year love affair. I am reliably informed that you can, as the grandparent says, replace most parts of them, but I have never needed to - they are very, very robust. Mine do look a little dog-eared but honestly nothing most people would worry about. And, obviously, they sound great.

extremely high end audio gear can usually be dissembled down to its constituent parts and rebuilt from scratch.

usually because it’s for industry professionals who thrash their gear pretty hard.

I'm not sure what the price point adds to it. Maybe headsets less than $100 are to be considered disposable?

Most of my headsets have detachable XLR cables, and some of them have replaceable ear cushions too.

Last week I took the ear cushions off my AKG Q701 (5 years old?), put them through the washing machine, and they came out great.

Pretty much all of them?

A lot of high-end headphones have interchangeable earpads, cables and sometimes even headbands.