You actually can: The Puya PY32 ranges from about $0.08 on up (well, $0.15 if you only want to buy 5, but the cheapest one is $0.0959 in qty 200 and $0.0676 in qty 5000+). ARM Cortex m0 in a 10-pin ESSOP-10 surface mount package: https://lcsc.com/product-detail/Microcontrollers-MCU-MPU-SOC...
Kind of mind-blowing. 24mhz 32-bit computer for under a dime.
But you'll learn more about the analog-ish world and not need to deal with SMD if you go the 555 route. And it'll save you power vs the astable monovibrator with NPN transistors.