StarTech USB 3.0 to Quad HDMI Adapter, USB Type-A to 4 HDMI Monitor Converter, External Video Graphics Card, 4x 1080p 60Hz, Windows Only, TAA, Laptops and Desktops, Bus Powered, 1m Cable

If they won't drop for mini PCs on each, HDMI over Ethernet or IP might be a better option, you can then run it from more unified setup. It's even possible to have one PC run many displays via USB to HMDI adapters. We use HDMI over Ethernet to run some of our digital signage like this which can go upto 100m or so point to point via ethernet cable. HMDI over IP can be anywhere your network is but the transmitter/receiver sets are more expensive. EDIT: something like this https://www.amazon.com/StarTech-com-USB-HDMI-Adapter-Type/dp/B09BJWGPXR If the PC has enough power it can handle more than 1 adapater too.