We've said it before, but it bears repeating: budget smartphones have become much more interesting than their high-end counterparts in the last year or so. While $600 flagships continue to get slightly larger and slightly faster and slightly better at a predictable rate, the amount of phone you can get for $200 or even $100 has increased by leaps and bounds. OEMs are looking to sell smartphones to people who don't have smartphones yet, and making things cheaper is the easiest way to do that.
Many of the smartphone OEMs offer budget models, but they're mostly either ancient or terrible. They have slow, no-name processors; not enough RAM or storage; old versions of Android that time has forgotten.