Does anyone know what is the cheapest (refurbished) smartphone this OS can run on?
Personally, I would aim a little higher though. I run it on a Pixel 4a and am quite happy. (Don't get the Pixel 4/XL since those do not have a fingerprint reader but only Face Unlock, which the latest LineageOS does not support.)
Unlocking the phone's bootloader is also not so easy, because you have to register your phone online and the web page is quite finicky. I had to try with different browsers to get the registration form to work.
Previously I had a Moto One Action and the system had a few quirks, but overall was OK.