A Google Pixel device with an unlockable bootloader. Carrier phones often come with a locked bootloader that remains locked, even if it is “carrier unlocked” and can be used on another network. In any event, you can get used Pixel phones relatively cheap. A pixel 9 pro xl with an unlockable bootloader starts around $400 for a 128GB and I just got a 1TB for $600. You can get a Pixel 6 pro for around $100.