Great question, guessing it's a fishing archer wep for sea serpents but that seems excessive. Must be the noob in me missing something.
It's for killing snakes on planes. Sub-Slayers :: Snake's Bane Anaconda Deep Sea Serpent Giant Serpent Ice Serpent Ice Snake Lava Serpent Lava Snake Python Sea Serpent Silver Serpent Snake
It's a the goddamned power house anti-Sea Snek bow. Bows are what, a 1 in 13 weapon type drop? So significantly more rare than let's say a Swordsmanship weapon. Then add my love for archery and fishing to the equation and you're looking at a highly underpaid bow right there. I would have doubled that price at least.