I just discovered the promotion for 4.3inch 800x600 HD e-paper display GDE043A2
edit: the promotion can be misleading: the price is per piece, not per lot.
and from first impression and experience, the 6inch e-paper is better!
The demo code shows some degradation of the white parts just seconds after update, and my first attempt with my adapted display class is worse, maybe caused by timing issues.
end of edit.
This display is easy to use with the demo board DESTM32-L
which has the special connector for this display, the special voltages the display needs for update, and a big 1MB FSMC SRAM on board. So the price of this board is justified, but still rather high (small production quantities).
I will add my ideas for a hobby solution with a black STM32F407ZE board.
This board has smd solder pads for FSMC SRAM on the back side. With smd soldering experience it should be possible to add the SRAM. Or the manufacturer could be motivated to produce a variant with the SRAM added.
Then we would need a connection board with the ATX526124 connector and the voltage generators, e.g. for connection to the FSMC TFT connector.
I found a connection board for the connector so far, not sure if I will be able to solder the connector to it:
The 6inch e-paper display has a 0.5mm pitch connector; slightly easier to solder to a board.
Could be a (small) business opportunity for someone to implement these ideas.