Flying in NZ is indeed fantastic, try and get down to the South Island if you can.
If time is an issue, you could get an NZ Class 2 issued by the CAA Aeromedical Centre at Gatwick (not too far from you), which according to the list of charges I have in front of me is £119. It took a week for me to get the piece of plastic from the AME in Queenstown (and I had to get a separate eye test), so bear that in mind if time will be tight for you.