RS485 opto-isolation

I am working with a RS485 serial bus. AFAICT, an RS485 bus works on a

The problem we have is that the run is very long - 2,000 feet or more - and adjacent to the main 480 V 3 phase power. We can get inductance voltages of 70V on a twisted pair measuring at one end with the other end nutted together.... (Separating them is not an option.)

So, I'd like to use opto-isoloators to protect the equipment. Basically, something that would provide only the appropriate 5V differential to the RS485 receivers, and also be fairly immune to high voltages due to inductance.

I'm thinking opto-isolators because I can't think of anything else... Other suggestions are welcome.... I need something very simple, easily produced in small quantities, and cheap...

Ideally, it would also work with a similar digital bus that uses 2 - 8V differential.... (I don't see why one wouldn't work with the other; if the optoisolators can can switch it, it should only be a matter of a different power supply to the bus side of things...)

Thanks,

--Yan