Nice flask. There is not always a simple answer on value - in this mold color density is important, I would want to see it in natural light. And of course condition is paramount - high point wear, other minor signs of age all detract a bit. One might give it a broad range of $600-1500...
I am sure one of the auction houses would accept this or you might sell it to someone directly but most anyone is going to want to handle it before buying.
