Hi sweety,
You need to contact the airline and ask them how much it will be.
Keep in mind that some airlines won't transport pets during the summer because of the heat.
You will also need a health certificate for the pets.
You may want to contact a consulate to find out if they have any special regulations for pets in New Zealand (quarantine etc...).
I hope all goes well for you and them.
What kind of animals are they?