The “terrible” 3 cent MCU – a short survey of sub $0.10 microcontrollers
These have their uses.A friend who frequently does contract development in the toy space has (or at least used to have) a favorite go-to MCU that costs under $0.06 in bare die.  It is essentially a 6502 with 100 bytes of RAM and a metric butt-load of mask-programmable ROM.  It was originally designed for greeting cards.  He has designed it into toys.It is hard to use, you need a dev kit and a good relationship with the distributor to get the documentation. It only makes sense in high-volume products, since it comes as passivated bare die so assembly requires a die-bonder and expoxy encapsulation depositer.Not for everyday use.  But as my friend says: “You haven’t lived until you have spent an entire afternoon arguing over $0.05 on the BOM.”