Anything less than 165cm total (height, width and girth added) is free. Generally, golf clubs and skis are free, too. So if you can, use a larger boardbag and call it your golfclubs when you check-in, with a smile on your face.
Otherwise, you'll probably pay $50-100 each way. Just remember when they ask that its LESS than 6' long if it is less. We use 5'5" double bags to pack board and kites and harness, etc. and the prolimit bags are not overly marked with logos, so we can get away with saying its golf clubs. Especially when you're flying somewhere warm. They never open 'em up.