Ask HN: Budget phone for timely security updates?

My Google Pixel is now (~15 mo after purchase, new) no longer receiving security updates. This phone was a gift; I generally buy used phones with long lives ahead of them. Google offers only $25 to buy-back a perfectly functional phone as credit toward a Pixel 3a.

The 3-yr lifecycle for security updates and lack of replaceable batteries appear to have killed off the used market for phones that receive timely updates. New phones appear to impose a substantial security tax: (Pixel 3a: $400, 28 months to end-of-life, iPhone 8: $450, comparable-or-shorter life?)

What are good budget options for ensuring a secure mobile digital life?