EInk have the patent on eink technology and their essentially a monopoly. As such the prices for EInk screens are never getting cheaper.

You can buy "cheap" EInk devices [1] with an ESP32 and flash your own software on it, an ESP32 costs less than 5$, so the rest of the price is all down to the price of the EInk panel and controller.

[1] https://shop.m5stack.com/products/m5papers3-esp32s3-developm...