There isn't a mid-range priced iPhone - although there is a mid-iPhone-range priced iPhone.
My phone is 4 years old, gets updates monthly, works better than when I got it and has a removable battery (replaced for £9 for an original part), very good camera, even by today's standards, hi-res screen, even by today's standards, huge SD card capability, even by today's standards, Qi charging (today's standard).
The list goes on, it cost £330 at the time and would sell for maybe £75 at best, like that will happen.
It therefore represents much better value than even a mid-range iPhone, whilst actually giving me the features I require (see above list). A removable battery and an SD card are not techie requirements really.
There are features that I would like (e.g. IP68), but I am not paying the premium asked for something that 'nice-to-have'.