That’s not how Android and AOSP work though and that is the foundation for both, firmware and GrapheneOS. You already have a disadvantage from moving away from the source, which is Google, so that even increases the effort react very rapidly to make up for that. All of that is not cheap.

I would assume you don’t need to go crazy expensive like with that phone now but to see that happening in the budget segment, where they probably invest next to nothing in software and security, just to get by, is naive.