Try to find a strange use case for Emirates.
If you have a 1st class ticket, you are entitled to 50 kg for a flight from SYD to AKL / WLG / CHC.
However, I can not know how much extra baggage would cost trans-Tasman if you had bought a 1st class ticket.
The weight limits seem to be here: https://www.emirates.com/au/english/before-you-fly/baggage/checked-baggage.aspx but I can not find the costs.
For example, an additional salary of $ xxx per year / kg