ESP8266/32 is slightly over a $1 but still within the spirit of “more like $1 micro”.

Confining more strictly to $1.00, STM32F030F4P6 (48MHz 32-bit M0) is in spitting distance to a 386 or 20MHz 68030 for some workloads. (50 MHz 486-DX2 was introduced in ‘92, but the typical desktop PC of 1992 was much lower spec.)

It was indeed the ESP8266/ESP32 I had in mind. The ESP8266 is slightly over $1, but not much! (e.g. available here for $1.17 https://www.aliexpress.com/item/32651747570.html)

Quite a few of the following options would give a 386SX from 1992 a run for its money in terms of raw computing power:

https://www.digikey.com/en/products/filter/embedded-microcon...

To compete with a high end 486 desktop from 1992 you might have to pay a bit more than $1, particularly if you want floating point.

Not to mention the lack of memory on microcontrollers.

MSP430 g series are under a dollar depending on what package you get. The DIP package is a little more expensive than the Smaller TSSOP but they are incredibly powerful.