Bicycle Mechanics - Cable Replacement

I just picked up an older bike, with friction shifters. Above the bottom bracket, the RD cable runs, it has no sheath, instead rubbing on some sort of metal clip (so as to make the bend). It rusted, and now the cable has snapped a few strands. Can I buy a cheapie cable from wallyworld, and reuse the cable sheaths? I don't think they rusted inside (when I shifted to a different gear, the cable looked shiny--bike appears to have been hardly ridden, just stored for years), so I figure, just reuse them.

Old bike like that should probably need new housing (sheaths) in addition to the cable wire itself.

You can try it. I've re-used housings successfully. But keep them in mind if you have shifting problems.

Cables aren't expensive at your LBS. Why go to Wally World?

Wally World sell a "whole bike" cable kit for around $5.00

Stainless steel?

Stainless or not, the cable on it right now is rusted quite nicely. It's my cheapie bike, the one I'm trying to keep costs low while I wait and see if I actually get into riding.

The LBS hours are only conducive to me on the weekends. I'll probably ride it as is for just a little while longer.

I wanted to reuse the housings, as I didn't want to mess with cutting new ones. This one has two sections of it, which is why its rusting currently. I don't know if the metal ends can be pulled off and reused on a new housing. And I'm a bit hesitant to ask what a new "proper" cable would cost, although it wouldn't hurt I suppose.

The problem with do it yourself cables is you need a cable cutter to do it right. Just using a side cut pliers tends to fray the cable ends.
I don't know what your LBS charges, but mine replaced the RDER cable (not housing) for $12.
I couldn't justify the cost of the tool for a "one of" job, plus it gave me the chance to support my LBS.