As others have mentioned, there are no good BifL options. Based on what I gather from your post, your best option is probably getting 2nd hand devices and following behind by a few years. You can probably keep a 3-year-old device for 7 or 8 years (which is ages in the smartphone world), then “upgrade” to another 3-year-old device at that time.

For this, I’d recommend something popular like a Pixel. They have a number of options for alternative OSes (Graphene and LineageOS are both good options) and they’ve done well for me as long-term use phones.

I’ve bought my last couple phones on Swappa, and I’ve had no issues with any of them. Sold one on there too, and they’re pretty vigilant (they manually review posts before they can go public).

I can’t be the only one who thought this was the Enterprise at first glance, can I?

I use it daily. My only complaint is that it doesn’t show up on Android Auto, but everything else is perfect.