Well, that's sub-$0.50. But yeah, CH32V003 is in that ballpark, and some of the cheapest Microchip and Infineon products are around $0.20.
It's almost never worth it to buy the cheapest chip unless you're making a million of something, but there are very good ones around $1-$2, and $5 is the upscale stuff.
Dave "EEVblog" Jones did a review of a (then) $0.03 microcontroller (Padauk) a while back (sorry, I don't know the exact episode).
Iirc an important caveat was that it was a one-time programmable (OTP) part. So you buy a bunch of them, programming failure or firmware-under-test doesn't work? -> toss the part. Of course that isn't an issue for a $0.03 part. But it can be an issue in terms of a board you want it on. Either that means discarding (breakout) boards too, or for development you'd need some kind of adapter to put bare ICs in.
Such annoyances only make sense for high-volume, low cost applications. Which is eactly where parts like that go in.
looks like Padauk PMS150C is back up to 0.08$, oh well :(
it's fun reading all the reactions to it (like "it’s cheaper to program a Padauk PMS150C to be a logic-level converter than to just buy a logic level converter"), but the magic is gone more-or-less
It's almost never worth it to buy the cheapest chip unless you're making a million of something, but there are very good ones around $1-$2, and $5 is the upscale stuff.