The PIC16C84 was the first microcontroller with electrically eraseable program memory. It was introduced in 1993. Before that, experimenting with microcontrollers required expensive windowed packages, and a uv eraser.
(Or there was the parallax “basic stamp (92), capable of running BASIC from a serial eeprom at the blinding rate of about 1k statements per second, for only abou $100 (including “programming dongle” and host-side ide.)
“About $100” eval boards were the norm until Arduino came along and changed it to “about $30.” And then came China with cheap clones and the ESP chips…