I know they have sold for 500. I wouldn't sell mine for any less if at all. I think Charlie asks a good question. The blue look much better and are much more desirable imo. I wouldn't pay a ton for the black/grey.
The moment I knew about them I tried their website..gone, phoned them...no luck. These sold out extremely quickly, so ebay was the only way, I got mine from a seller on French ebay, the Black/Grey about £290, the Black/Blue about £270, but as only 30 of each were made I would imagine most are rooted in collections by now, and I haven't seen either for sale for some time. They are both fantastic pairs, but would like to have seen them with relating, rather than the usual pink microbags.
I sold a pair to a member on here about 2 months ago, and they crop up from time to time.
What's their value? As stated many times, value is an individual thing. One mans treasure is another mans trash so you should pay what you're willing to pay, not worry about what others think the price should be.