And there seems to be no way to buy a "free" smartphone without Google Services and telemetry below $250. Why 250? Because free OS have multiple bugs and issues and it is not rational to pay more than that.
I am considering two options, one, try to clean up and patch the firmware for a cheap smartphone (remove almost everything proprietary including Google Services, Unrusted Execution Environment, except for basic GUI and launcher), or two, port something like Lineage OS to my phone. Also I need to examine the network traffic and scan for potential weak points like SUID binaries. It is scary to think how much time I will have to waste for this.
Also, it is pretty stupid, in my opinion, to make an OS not based on Android, for example, use Qt for GUI, because there will be no apps for it.