WaveShare announced a new 4.2" 400x300 and 7.5" 800x480 NFC-powered E Ink devices. The idea is that these can be used as small monitors that do not require any batteries or power.
These devices can be updated via a smartphone that supports NFC (via the NFCTag application). Screen refresh rime is around 4-5 seconds. The price of the 4.2" model is $39.99 and the 7.5" model is $68.99. Waveshare says that not all smartphones will have a strong enough NFC to connect to the devices, but Waveshare offers a dedicated NFC board with a micro-SD card for $22. These devices also ship from Amazon.com, costing a bit more than directly via WaveShare.