cacahuete

For the Auckland consulate, the beneficiary will pay NZ$455.00 at the interview. This can be paid in cash or by bank/cashier's check (NOT personal check) only. The details on this are in Packet 3 that the beneficiary will get in the mail.
Packet 3 is a checklist that is mailed to the beneficiary. Once the beneficiary gets it they need to gather all the documents, sign off the checklist to confirm they are ready to set an interview date, and mail the checklist + documents back to the consulate.
Once the consulate has received and reviewed Packet 3, they will send the beneficiary Packet 4 which is just a letter with an interview date.
The Auckland consulate seems to be pretty quick to respond with Packet 4 once they receive Packet 3 back - it was only eight days from when I mailed back Packet 3 to when I received Packet 4 with the interview date. And then the interview was only 18 days later, quick compared to a lot of other consulates.
For Packet 3, the beneficiary will need to mail in all the documents on the checklist except for his passport, the visa fee and proof of relationship, which is brought to the interview. This is noted on Packet 3 instructions.
If you haven't done so already, you will need to download form I-134 (can be found on USCIS site), complete this and send to the beneficiary, along with proof of your income. The beneficiary needs to mail this in with Packet 3 before an interview date is given.
The address to send your Packet 3 to will be noted on the Packet 3 instructions.
If the Auckland consulate has received your petition from NVC then it shouldn't be very long at all until the beneficiary receives the Packet 3 instructions.

Journeyer,
I faced the same dilemma you did a couple of months ago.
I also was on a B-2 visa although I was luckier than your fiancee and was given six months at entry and then approved for a six month extension.
Over the last couple of months I was there I seriously considered marrying and adjusting status. I went over and over it in my mind but in the end I decided that the safest option was to return home and apply for the appropriate visa. I felt that the months of worries I would experience as I wondered if my AOS would be approved or not were not worth the few months I would have to wait if I returned home as I was supposed to.
I have paid US$450 to change flights before.
But do you want to take a risk or do you want to pay that amount to feel safe? That is the question to ask yourself and your fiancee.
My fiancee and I filed the paperwork for my K-1 visa the day I left the country. Today, it is already exactly two months since we filed the petition. Time passes much more quickly when you know it is the last time you will have to be separated.
A separation is not necessarily a completely negative thing. The separation would give your fiancee time to tie up all her ends in her home country and say goodbye to her family.
My fiancee and I were separated for 11 months between my two trips over there. We thought we couldn't stand being separated either but we worked through it, we had our own lives and our own things to work towards and of course we had my next trip over there to look forward to. In the end I think we were better for this test that we passed.
Your fiancee has only been in the US for less than a month and marrying after being in the country for less than one month could be viewed negatively by USCIS.
In the scheme of things, a few months is not really that long to be apart when it's the last time you'll have to be apart.
You are fortunate that you would be able to visit your fiancee at all while the visa is processing, many people on these boards are not as fortunate. You are also lucky that you have been able to spend as much time with your fiancee as you already have, many people are compelled to make a decision to marry maybe earlier than they would have preferred to, in order to continue their relationship and live together.
I will not be able to see my fiancee again until I have the K-1 visa. I cannot afford it as I need to save my money for the first few months I am there before I can work and I am unable to get time off work here. In addition, I would not want to risk spending the money and being turned away at the border. He cannot visit me as he also has work commitments.
For me, the most painful part was the decision whether to leave or stay and adjust status. Once I'd made the decision to leave, I accepted my circumstance and everything became easier.
Yes, it is lonely here by myself without him. But I have found I have plenty to do between work and tying up all my loose ends here and spending these last few months with my family. I don't need to worry about whether my AOS will be approved, I just wait for the visa, patiently and with peace of mind.