This is getting confusing, and I am not going to comment on price in absolute terms or in comparison to other builders/makers/etc., but Cardas makes different cables being used for headphones.
The traditional Cardas cable was the sky blue one that I think is now sheathed in a gray cover instead. I never thought that cable was the best match for the HD650 but I do think it is pretty good with the HD600. I don't know exactly why or remember the differences so much, but there you are.
The newer Cardas cable being used by Headroom and maybe others is the Cardas Fat Pipe cable, which is physically thinner than the old sky blue one. I think I first heard these at the New York national HF meet so they aren't that new but HR is now offers recabling formally on the site. Anyway, they say that the Fat Pipe uses Cardas's Constant-Q, Golden Ratio configuration. According to Tyll's marketing folks: "he Fat Pipe geometry is a four-conductor with braided shield cable featuring Golden Ratio, oxygen-free, pure copper Litz wire with pure teflon dialectrics just like the big boys. The connectors are terminated by hand using Cardas Ultra Pure Quadeutectic solder. The connectors are mechanically inert, isolated from electrical noise and completely resonance-free, producing a very quiet, musical and superbly accurate cable capable of beautiful sound reproduction." I liked the impact of this cable on K701s, although I frankly cannot recall hearing the HD650s with it.
Here is Wes Phillips' on-line article about the Fat Pipe recable. He liked it on both HD650s and K701s.