air transport – Emirates trans-Tasman, extra luggage?

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: but I can not find the costs.

For example, an additional salary of $ xxx per year / kg