A low drop rate + 8th boss in + normal/heroic mode only + added to the game months after ToT went live + few people are doing ToT nowadays = a hard to get, high priced pet.
According to The Undermine Journal it has never been listed in any of the Trollbane-US auction houses. I've got a lot of gold tied up on both my Horde and Alliance alts in case one ever shows up. That's because somehow I have offended the RNG gods and I know it will never drop for.