24VDC and RS-485 in same cable?

If you use instrument cable with individual twisted, shielded pairs it will work just fine. There will be no cross talk between pairs, that's why they are twisted, to minimize magnetic coupling, the shield prevents electrostatic coupling. Of course you have to be careful to avoid ground loops by grounding just one end. I prefer the control system end although there may be a reason to do it in the field.

If you find there's a problem with the RS-485 reduce the baud rate.