That's one of those impossible to value items. At this stage of the game, barring any unexpected bid wars, it'll be worth whatever Gregor will pay for it. He's the gothic defender guy after all.
If you really want numbers, I'd say 500e range, but it will depend on demand.
Could see 500e possible as the skin is popular and very nice, not tons of these around, but I'd agree on the 1 off and strength and enchant combo hurting the value, of course.