Long Distance, Hard Wired Communications

coax

You can use coax over longer distances with hugh success,Rg54 typical, and is cheaper to maintain by yourself than optic fibre,unless if you got the gear to do your own optic tail end terminations.

How fast are you going? For limited speed comms, RS422 or RS485 can be good options for your kind of distance (and a lot more).

Go fiber!!!

Yes Fiber.

multi-mode is cheapest and will run 2000 meters without repeaters.

SynOptics has FDDI that may be able to be your solution

Among others.

If the speed is not an issue you can use copper wires with modems or GDN-s, otherwise the solution is the fiber.

Multi-mode fiber given this distance is your best bet...and will be cheaper than coax.

I have used US Robotics modems over AWG 22 UTP wire up to 3000 meters with no problems. The biggest concern is that modems (and most long-distance copper solutions) are getting harder to find as fiber costs continue to drop.

Wireless is another alternative you should consider. Many utilities in the US use spread spectrum radio for SCADA telemetry. It can reach 10 miles. Microwave Data Systems is one source I have used in the past.

RS 485 for non critical data or CAN bus for important stuff.