There are two essential bits of knowledge to cables in hi-fi.

Different materials have different conductivity. Most commonly used are silver, copper and aluminium (those fancy-looking overhead rails in AKG headphones are made of aluminium). Of those, silver has the best conductivity and retains most of its conductivity even with its surface oxygenated (silver doesn’t get as oxygenated as other metals - it doesn’t rust).

Oxygen molecules in cables, especially made of metals that are vulnerable to oxygenation (copper, steel) tend to break conductivity (oxygen atoms interfere with metal molecular structures in the process of molecular diffusion, which may end in complete breakup of metal - as with heavily rusted steel). Hence a special process in which copper cables are formed with as little exposure to air as possible, creating non-oxygenated or Oxygen-Free Cable (OFC for short).

Hence the answer to the often-asked question - whether different cables make any improvement. They do, silver being the best material for any parts and interconnects (some of the finer amplifiers, like the Ongaku, were built mostly with materials like silver).

There also are different alloys, combinations of silver and copper, less common metals, and so on.

Just how much of an improvement a headphone cable is going to make depends, obviously, on original cable, headphones’ construction and source. Here the general rule is effective - the less distortion every component in the sound chain introduces, the cleaner the output. This also depends on how much a manufacturer has saved for himself from cutting making costs #:-)

So what’s a decent price for a cable? The short answer would be probably anything under $200, better under $100.

Head-Direct sells several cables which aren’t likely to empty the bank account: mini-to-mini interconnect cables, IPod line-out cables, and cables with connectors for Sennheiser headphones. Unfortunately they don’t sell cables terminated in Mini-XLR connectors for AKG headphones, but there is an EBay merchant selling Sweetcome cables at a rather good price.

Or, one could arm himself with some tools, get some proper connectors for headphones (maybe even salvaged off old damaged cables) and get some silver wires or cables from a cable dealer, which is likely to be much less expensive than audiophile-targeted cable with cost in the hundreds or even thousands of coins.