Cables for LVDS RS-644
You could probably go the same route that Power over Ethernet (PoE) goes: Have the supply voltage be a DC offset on pairs of the cable, and couple in your receiver through transformers with a center tap on the biased side.

5m sounds a bit much for LV differential, but that really depends on your equalizing abilities.

Also, at some point, the overhead you're incurring by extensive cabling and dedicated differential transceivers might be more than it's worth – assuming your application could withstand the latency, have you looked into using one microcontroller on each end of your 5m distance, translating the unidirectional signals, clock and chip select to a bidirectional bus? I'm thinking about a really minimal system based on USB (that's the cheapest long-distance bus that comes to mind). Or, CAN, which is actually designed for this kind of problems. For both, there's cost-efficient MCUs that come with integrated PHYs.