Rear mech

[Ajax Bay]

I recommend buying a workshop box of 50 or 100 inners

I wonder if learning and practising indexing a rear derailleur might worth it as a first step (for the OP not you ), before a mass purchase of cables. And such bulk purchases do reduce the opportunity to visit, with a packet of biscuits, one's LBS.
Still just think how pleased your legatees will be with their share of the residue of your box of cables.

 

[slowmotion]

As I said.
If you follow the video, do as it say's by starting from scratch, you can't go wrong.

It's by far the best clip about rear derailleur adjustment.

 

[Blue Hills]

Still just think how pleased your legatees will be with their share of the residue of your box of cables.

possibly but will still have been cheaper fort me on this earth than buying them singly.
gear cables go quite easily at the business end I think whatever your skills - you need to keep an eye on them.