Interesting review of $1 microcontrollers

A well presented and through review.

Would like to mention that some of the FPGA soft core processors have an incremental cost under $1 and have full tool chains: ZPU and some versions of RISC-V.

Many of the legacy processors not mentioned by Jay Carlson also qualify (soft-core version with under 1K LUT count: 6502 ...).

If you don't mind programming in Forth, there are stack soft processors that scrape the bottom of the cost barrel. They reach a LUT usage level where you can use several of them assigning separate tasks to each one rather than worrying with multitasking.