Hey, thank you both! $32 is very likely beyond our budget. As we still have some time to procure these, I was thinking about getting Pi Zeros (hoping they become available in bulk any time soon) and use USB Ethernet adapters and the unpopulated composite video header they offer.
In the end we do not need any fancy Xdmx setup. I will try to use multiple setups of Pi Wall (
http://www.piwall.co.uk/) to get a video signal to all of the screens.