I would be interested to know the answer to that question, too.
Personally I obtained a UK/EU main head unit (which incorporates the tuner) from Ebay for a price less than the "experts" in NZ charge for their possibly dodgy conversions, and then just had to update firmware to latest (not strictly necessary), and have component protection removed. Very happy with the outcome
Like to know how these conversion are dodgy?
If you are lucky enough to find a unit that has the tuner included (bigger than an A3, or the new MIB and they are separate units) and one that isn’t blacklisted by Audi’s ODIS system, and you have the contact to remove CP then you can convert it cheaper.
Otherwise for 2G:
1) Replace radio (Japanese hardware is totally different)
2) Replace NAV (Japanese hardware is totally different)
3) Flash new firmware and burn map discs
For 3G/3G+:
1) Replace radio (hardware won’t pick up NZ frequencies) - and also have to remove CP
2) Change main unit eeprom with correct language packs
3) Change firmware to make the hardware know it’s a Eu/ROW unit (hardware is the same, variant is different)
4) Install maps
5) Activate maps
6) Fix maps database else you’ll just get a ‘database is initialising’ error
For MIB:
1) Find unit and then get it converted by VIN locking it to the new car (good luck)
It’s an involved process that the majority of people who offer this have spent a few years doing so. You’re not paying for the hardware, it’s the knowledge of how to do this plus recover in the unlikely event it goes wrong.