Waveshare sells 1 to 13-inch panels for 7 to 540 USD: https://www.waveshare.com/product/displays/e-paper.htm

Pixel density isn't as good as say a nice Kindle, but they are usable. I've played around with one of their 1.5 inch module

You can buy old 6" e-reader panels for ~22+ USD https://www.ebay.com/b/ed060sc4/bn_7024905630

See https://spritesmods.com/?art=einkdisplay for how to drive them.