Originally Posted by jarinzfin
I upgraded Y -> C at AKL checkin, they charged the difference between paid fare and lowest C fare, which at that time was only NZ$300 for AKL-MEL!
So you paid the lowest C (J) fare. I do not see a saving.
I would buy the lowest J fare in advance, to make sure I will have a business class flight and can select the seat I want to sit in.