Sounds like an ideal use for the venerable RS422 bus, just use either 2 twisted pairs, with one providing a ground reference, as you really want to keep in the middle of the CMRR of the differential receivers. Or use a microprocessor at the ends that has an ethernet PHY in it ( 10/100M will be fine, and ultra cheap from the switch side) and POE for the system, using a central POE switch to power them.
That way you have both easy connection ( cheap cables and connectors) and with ethernet and POE you have some power at the nodes, at least enough to power sensors and such, even small displays and perhaps even small low power actuators, without needing power cabling.
Even going RS422 use cheap Cat5 cabling and connections, so you have redundant pairs and can transfer power down the spare pairs as well, if you can live with the cable loss.