The going rate is about $4800 for a mint Qualia 010 here, which is what I paid for mine (didn't come with the box, silk, or papers... just the headphones and stand and a second pair of different colored pads). I'd say $5000-5500 would be right for a complete set, blemish free, and under 20 hours or use. $5800 is pushing it though, and higher still is getting into flipper territory.
Obviously with something limited to only 250 examples we're talking one of the highest levels of rarity (along with the HE90, SR-Omega, HeAudio, PS-1, LCD-1, etc.). So someone is probably going to give in and pay that price, and that sets an unfortunate precedent for future Qualia sales. Price just goes up, up, up.
It's not quite the gamble that buying the R10 is, as there's less variation and age-related issues with the Qualia. However it's still a very fragile headphone and it's still Sony we're talking about, so no replaceable parts. Good luck finding another headband for instance...