The Maxim 1480 is abbedesolutely wunnerful for such applications, for full duplex, you will need 2 at each end. If you are not using a lot of power at the remote end, use a 7805 as your regulator, it is cheap and will do the job (perhaps with a series resistor). If you are going to use a switching regulator at the remote end, make sure you put a large capacitor - or better a C R C filter in the 24 V line so the switching current does not couple to your signal wires.