This isn't perfectly within your search criteria, but you may still find it interesting. Just today I researched the available solutions for driving a ED097OC1 (compatible) display, which was built into the Kindle DX, has a diagonale of 9,7" and can be obtained for about 30€ [0].
There are some projects dedicated to driving the screen with an ESP32, which already has WiFi built in, has good low power modes and is pretty cheap as well [1] [2].
There's also a project driving e-ink displays with an stm32 [3] and one to do it with an FPGA [4].
Beyond 13" things get really expensive and hard to find - best I can do is 12,48" for 150€ [5].
[0]: https://aliexpress.com/item/32983492389.html
[1]: https://github.com/dqydj/PaperBack_EPaper_Display
[2]: https://hackaday.io/project/168193-976-e-paper-controller-ki...
[3]: https://hackaday.io/project/11537-nekocal-an-e-ink-calendar
I don't know specifics about the voltage conversion yet (these screens need about -20V - 20V), but I reckon that if you're really frugal you could make a battery powered wall display for under 60€ with this stuff - and that's part 1 of what I'm thinking of doing.
Part 2 would be to stick in a Pine64 SOPINE System On a Module [6], put on a capacitive touch layer [7] and run a mainline Linux with KOReader and maybe even a Wayland compositor to be able to run any Linux app (the high contrast GTK theme seems perfect for this application).
All hopefully for under 200€, which is a lot less expensive than other e-readers if that size and a whole lot cooler.
Any tips?
[6]: https://store.pine64.org/?product=sopine-a64