Air New Zealand operate the piece system out of Maui – you get two pieces up to 46kg total. After that it’s USD$85 per piece, or USD$30 if a bag is over $23kg.
The only catch is that they list the maximum bag length as 250cm, a little shorter than most airlines who quote 270cm. That shouldn’t be a problem with most modern kit, though it can be tricky to get a board bag as short as modern boards.
Overall it’s a great deal, they’re the cheapest other than Air Pacific for some routes. I should be flying with them so will update when I’ve done it first hand!