In todays mail:
2 more RockPi 4B+ SBCs from embeddedcomputers.ca (2GB RAM and 32GB eMMC on board). They cost $54 ($27 each), including shipping and having Linux pre-installed on the eMMC. They keep going out of stock, so someone suggested using this site to track the changes automatically:
I've never used this site before, but it's worth a try.