This of course doesn't really resemble Arwen's actual mourning gown from the Peter Jackson trilogy and rather comes from us saying "Think of Aragorn being dead!" during the photoshoot (which replaced last time's "Think of the Weight of the Ages!"). Wandering away from Tolkien, I suspect this may look rather fetching a drow character, with perhaps a dash of classic purple or red in the accompanying clothing and I can't say this wasn't made with appealing to that sort of aesthetic in mind.
To commission a similar coat from the Mercenary would cost in the region of £90-100. The prototype of the chase dress itself (UK women's size 16-18) is available on Character Kit for £90.
In Other News: You should go wander over and have a look at Gracewing's Clockwork Firebird Designs, now with added updates. Photos of the amazing Catbus, Red XIII, the awesome spider-butt and more. (And of course, there's a spot of pride that she's wearing the steampunk velvet tailcoat with the beautiful Crown of Gears Leather Corset.)
More photos of the coat under the cut.