TL;DR
- Efforts like Graphene OS face increasing pressure from apps that refuse to run on non-standard Android.
- The custom ROM project characterizes Google’s approach to device attestation as incomplete and flawed.
- Graphene OS is prepared to take legal action if Google won’t let it pass Play Integrity checks.
The Pixel 6a is really cheap on the used market, and it still gets updates for at least 3 years.
The 7a isn’t that expensive either. I recommend staying away from Fairphones, Murena or /e/OS as these are highly insecure, and the companies behind them have repeatedly proven that they don’t give even the slightest fuck about the security of their users. They don’t publish important Android security patches on time, and Fairphone even managed to fully break Android Verified Boot, by signing their ROM with the publicly available (!!!) AOSP test signing keys. It should have been impossible to pass verification, but the vendor conducting the verification seems to be just as incompetent.
A used Pixel with GrapheneOS is your best option, while still being affordable.