I replaced my old iPhone XR with a brand new 16 this year, not because anything was wrong with it (even the battery was OK), but I wanted to see what the changes brought.

I was quite surprised that other than the much better battery, USB-C, and much better camera, and sometimes faster speed, the old one was holding up quite well.

You can get an old iPhone XR for 100 EURish, in decent condition. I really have no idea what model year iPhone's others have.