First off, the "top" tier red tunics are over-powered, though as a mage I do love the idea of having such a superior best-in-slot item. With that being said if the item is not taken out of the game then my suggestion(s) are:
1) sell for 300 ED as per suggested on wiki for quest items. I was cited that you can buy one for 300 ed but it will have random skills as if you turned in a mirror shield. The counter argument to this is that you can purchase a travesty mask and specifically ask for the type of +skills you want on it.
2) sell mirror shields on the token vendor for approx 750k tokens. The reason I suggest this is based on this logic: the number of +skill magical clothing provides for approx. 55 different skills (there are 58 total but there is no clothing for imbuing, mysticism, throwing, spellweaving) skills but , ranging from 1-10 with 8 different slots (feet, pants, skirt, half-apron, shirt, sash, robe, cloak). This makes the chance for getting the ONE item you want in the correct slot, skill, and +amount: 1/4400. The math for the red tunic is as follows: there are 4 different "listed first" skills (magery, wrestling, chivalry, meditation), 1 "middle listed" (resist), 3 "bottom listed" (eval, itemID, spirit speak), all skills in intervals of 5, 10, 15, 20. You have the chance to get either Int or Dex at 5, 10, 15. That being said, there is a combination of 288 different types of tunics you can get. The fact that the RESPAWN timer is over 4 hours makes the chances at getting the exact one you want very difficult. If you were to get the mirror shield every time it spawned all day for 48 days straight then you have the chance to get the specific one you want. All this being said the chances are 1/288 to get the one you want. The reason I have it at 750k tokens is because the chance to get the ONE magical cloth item is a little over 15x less likely than getting the red tunic you want. That being said, make the mirror shield available for 15x more expensive than the magical cloth deed and there you go as far as having it be equivalent as far as randomness and chance goes.
3) Just make the respawn timer from over 4 hours to something manageable like 15min.
Finally: i understand that a 20/20 mage/eval tunic would be a HUGE seller of ED at auctions but if ED is flooding the server wouldn't it make more sense for 50+ people spend 300 ED (15000 total ED) for the item rather than 1 person spending 1k-2k at an auction once a month? (assuming the item is put up for auction, that 1-2k number is just an estimate of what I think people would pay for it)
