What is your expenditure threshold for the best smartphone in the market? At what price point does a smartphone start giving diminishing returns?

I spend between $100 and $480 on my budget phone. Just check on Samsung Galaxy A80 and its distinctive characteristics like rotating camera system and unique pop-up. They might miss out on some high-end attributes e.g., reverse wireless charging. But overall, you get (70 - 90 percent) experience in comparison to flagship phones that their cost ranges at $1,000 and more.

Almost all phones cater to primary needs at this range ($100-$480). Generally, the majority of phone users phone, text, surf, and take photos or selfie. And with the new era of $1,000 plus phones, I don't think there is a diminishing point at all. However, the opinion would depend on the purpose or interest a consumer intends to serve. For example, the Galaxy A5 2017 costing about $350 has a very nice battery life, speed, very stable, and quality screen. But the only reason one would go for a high-end budget phone is the need for a top-quality camera. Either way, I am sure my next phone will be a mid-range smartphone.