> I just want a cheap phone that can run like five apps (sadly one is the type that won't work, i.e. payments), and not run Android or iOS.

https://devices.ubuntu-touch.io

https://wiki.postmarketos.org/wiki/Devices#Community

you can certainly buy some of the supported smaller devices (e.g. Pixel 3a) and change battery for new

sadly basically nothing newer than 2020