The Un-Sets, imo, are really something that ought to be kept around as they offer freedom, creativity and forward/very forward thinking
The title of most expensive means nothing if no one will buy the card
Like most Pokmon cards, the value of Froslass depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Legends Awakened)
Of course, as I always say, a card is only as good as the context that surrounds it, so if there are not that many good fighting attackers, Barbaracle wont be as strong but I honestly think it is a fantastic option that immediately makes new fighting types a greater threat
However, it still remains a prize for collectors