Hi alex1pdx,
Here is a link to s2's site where you can check out their prices, depending on what exactly you want doing: s2-audio.com
You could also just PM Scott from s2, warrior05 a few messages up and he can give you a quote, he normally replies pretty quick and his customer service is great.
I went for the 5 foot re-cable with nylon sleeving and the sound chamber treatment. In my opinion on SQ it was worth it, as many other head-fiers have agreed, it just relaxes the over pronounced high's of the HFI-780's, don't expect mammoth changes, it is subtle, but the main thing for me is that I can listen to the headphones for much longer periods now without my ears becoming fatigued
I think other members have noticed more benefits than me from a re-cable, I guess it all depends on your ears.
Aesthetically, the re-cable is a great idea, the stock cable just used to coil up in a big birds nest, which I hated and it was far too long, the new one looks professional and is impossible to get in a tangle.
Also I live in europe, so shipping obviously cost a bit more, but to any other people on this side of the pond, s2 are happy to deal internationally, I couldn't find any re-cable options in europe.
Make sure you've given the 780's at least 200 hours burn-in before you make you're decision as this changes the sound quite a bit, but I guess you've probably already done that after reading other people's comments in this thread.
Well this is getting a bit long winded, so I say, if you've got the spare cash, a recable is worth it from s2.
Cheers