In May/June 2006, I hunted in NZ. I flew with Air NZ on both International & Domestic routes and had just on 30kg of hold baggage, plus cabin baggage and only an economy class ticket. I did not have to pay any excess baggage charges. The trick is that when you book your tickets, you make sure that you tell the booking clerk that you are travelling with firearms and that you require their complimentary "Sporting Equipment Baggage Allowance" for the transport of your firearms. The Sporting Baggage Allowance will get you an extra 10kg's of hold luggage for free.
I and a mate who travelled with me had absolutely no problems with Airline Staff and found them to be most helpfull. I can honestly say that I have always found Air NZ to be a firearm friendly mob to deal with.
Hope this is of assistance
Rod