I just found another vendor carrying E-ink monitors. (Thanks, source!)
The electronics parts warehouse Waveshare is now carrying an unbranded 10.3" E-ink monitor (1404 x 1872 resolution). It costs $540 plus shipping.
Unlike most of Waveshare's products, this is more of a retail unit than an electronic component. The monitor comes equipped with a USB port (for power) and a mini HDMI port (for data) but no frontlight or touchscreen.
It supports three display modes (GC16, A2, and A2+), offering the option of high detail (GC16), monochrome black and white (A2), and something in between (A2+). This gives you the option of trading display quality for speed, and vice versa.
You can change the mode or refresh the screen using the two buttons below the screen to the left, and you can also change the contrast using a nob on the left side of the monitor. (I do not know what the thing on the bottom right corner of the monitor is, hwoever.)
I don't yet know who made this monitor, or what the performance is like. If you get one, let me know.
Thanks for letting people know about this (I sent you the link).
That thing on the bottom right corner, as weird as it looks, seems to be a through-the-frame hole, possibly for a pen to use as a stand: https://www.waveshare.com/media/catalog/product/cache/1/image/800×800/9df78eab33525d08d6e5fb8d27136e95/e/i/eink-disp-103-5.jpg
Another monitor (LCD though) on the Web site also seems to have that: https://www.waveshare.com/media/catalog/product/cache/1/image/800×800/9df78eab33525d08d6e5fb8d27136e95/1/2/12.5fk-4.jpg
I didn’t see that one photo, thanks!