I just sold an ancient but working iPhone 6 on eBay for $22.50. I got a new-to-me iPhone SE (2nd generation) to replace it for $89 from Gazelle, so my net to move from a phone first released in 2014 to one that was first released in 2020 was $67.
My daily driver is an iPhone 14 but there isn’t much that I would miss by using the SE in that capacity. The 14 has a much better processor and camera than the SE but that doesn’t make too much difference in daily use. The biggest impactful difference is probably battery life but even that is not a big deal as they both need to get charged on a daily basis.
What I was most surprised about was being able to get anything for phone that is almost a decade old and out of support (although Apple does release security patches for it). It’s nice to not have to landfill something and that iPhones hold their value so well.