You'll find an endless array of opinions here, so I'll offer mine with the caveat that it's one of many: there are cheap cables, good cables, and snake oil cables.

I played around a little bit with speaker cables a number of years ago, spent more than I probably should (the cables on my front three probably cost me $400 total, maybe a bit more). In addition to those cables (an Australian brand called TMC that I picked up used on Audiogon here and there), I also tried some BetterCables and a loaner set of Transparent Music Wave Super's (latter being worth over $1000 at retail for a two-meter pair). I've also bi-wired and am still doing so because I found some subtle improvements (and because I've got the cables anyway at this point) but I think that as long as good cables and (for bi-wirable speakers) good jumpers are used it's hard to make a real definitive argument in favor of bi-wiring. While I feel very comfortable knowing that I don't have any worries about my cables' shielding, resistance, or impedance after the tinkering that I did over the course of a year or two, I also came away feeling that I'd explored deeply enough to rub the shine off of the notion of exotic cabling. Those pricey (at least by my standards) speaker cables are the last cables I've bought that didn't come from either Outlaw, Blue Jeans Cables, or MonoPrice (a handy source for really long optical cables).

The notion of basing cabling cost on system cost is pretty suspect to me. I'd counter that it's best to buy the cables that are appropriate to your need. In the online market, I've had very good luck with everything I've gotten from Blue Jeans Cables - they're a no-nonsense sort of outfit that use quality materials at a fair price. I've also bought from BetterCables, but I felt that starting somewhere around the time of the Silver Serpent line they started moving away from their original intent (which was to do what Blue Jeans Cables does - make good quality cables at a good price with no marketing fluff).