If you are looking for a super cheap replacement for something that lies between an ATTiny and an Arduino Mini, and costs around the same as the ATTiny; you should have a look as the CH55X based boards available these days. I was able to get a handful from AliExpress for $1.31 each. The CH552 comes in a cute 20 pin PCB with two 10-pin headers that need to be soldered on to the board. That makes it useable with a solderless breadboard.
You wold notice a 24 MHz crystal being used as a clock on the board. Here is a closeup of the USB-C type board after assembly and running the infamous “Blink Skech” for Arduino. The CH552 board comes with a reset button, another general purpose push button and an LED that can be seen illuminated in some of the photos.
For those of you who don’t know what MCS51 is all about, it is the generic name for Intel’s 8051 8-bit microcontroller family. The CH55X series of microcontrollers make use of a 8051 core as their processing engine and that makes them different from the AVR based or ARM M0+ based Arduino boards.
This interesting new family of chips ranges from CH551 all the way up to CH559, which is the highest end member.
This link can be added to the board manager for getting your Arduino IDE ready to work with CH55X boards.