The STM32F103C8 is a good example. If you buy a few dozen off of AliExpress or TaoBao, "blue pill" boards containing them and a microUSB connector cost less than $3 each.

They only run at 72MHz, and they don't have floating-point hardware, but the price point means that you can give them away without a second thought. When someone has an idea for a Halloween decoration, or a garden sensor, or a proof-of-concept, it's usually my first choice because it costs less than a coffee.

Once it stops getting rained on, and corroded, and coated in dust, and submerged, and fried by a squirrel who thought wires were edible...then you can reach for the top of the line.