Copper is a commodity in itself, but not the cables, copper prices fluctuate on a daily basis, a cable has more components than just copper and manual labor to assemble it, so don't count on copper being a commodity as your sole arguement for all cabling being over-priced. And Mid, I say this with no malice or any sort of sarcasm.
Here's what some "pro" users have experienced with less expensive cable, in this case XLR terminated microphone cabling:
"These Musician's Gear microphone cables are good while they last; that's about all I can say about them really. I got a couple of them when I ordered my Phonic PA system from here because they were cheap and I figured I could use them. They lasted me about 3 months? If you're just gonna need to use a cable once or twice, go for these, but if you're gonna be using them for an extended period of time, look elsewhere."
"Bought 2 15 ft cables for our Youth Worship Team. These do not get much abuses, as they are used 2x per week and stay plugged in most of the time. Both cords failed within 9 months. Since there seems to be no warranty, we cannot return them. At the same time I bought 3 Horizon cables that were more expensive and used for exactly the same purposes. All 3 Horizon cables are still working."
"I bought (6) of these in June 2006. All (6) cables, within the last year have shorted out or had an internal wire break. Impedance check shows soldered connections are not crossed and are good. The wire break is in the middle. Not happy with product."
I bought 2 12 foot ones for my karaoke set up. They worked great for about 3 weeks, after that, they crap out. However, I did get one of 6 foot cables for my DJ mic and it works great, but that mic doesn't move all night. In end I've having to spend even more money to get good cables."
These were just plain copper cabling as used by musicians anywhere, but where they failed was the the build quality.