If you are going to string one wire you may as well string a double wire, like doorbell or speaker wire. If you use RS485 protocol that will be fairly resistant to noise.http://www.gammon.com.au/forum/?id=11428
With just two wires you could "drop" each station off the same pair of wires, and have the master station send down a query, go into listening mode, and get a response back.
Another approach would be to go wireless, if each station has a solar panel. If not, you might want to have a second pair of wires to send the power down to each station.