Speaking from AB market, if you are talking about the Legends of Norrath cloak that increases your size when you use it then it's worth anywhere from 500m-1 Krono/Current krono value in plat. Obviously you have to find a buyer though and that might come easy, might be hard. If your talking about LoN cloaks in general the vast majority are worthless. Only the growth/shrink ones have any value.
Not necessarily, it should be roughly same value as Growth cloaks. That being said, if I put it for sale in Auction chat and someone offered 500m I'd jump on it.
