i've bought complete hunter's garb sets a few times at about 8m.
i dont recall off the top of my head if the gorget is the only rare piece, or one of two. if its the only one ild price it at about 5-7m, if its one of two then about 3-4m.
Although as the sets and the rare pieces are not often for sale they could certainly sell for more or less and therefore the rare pieces could certainly be valued differently.