fair enough - the USB-CAN modules can be expensive - there are cheaper ones on Ebay but I don't know how good they are
probably worth looking at an ESP32 though
on Ebay in UK ESP32 modules are about £6 and a tja1051 CAN transceiver is £5
thinking again - you could build a point to point network layer on top of Canbus - assigning addresses to nodes and transmitting packets between them
the nodes could use the Can filters to only receive the correctly addressed packets