In reply to abr1966:
Partly depends on trip duration. The shorter the total trip, the less time you want to spend travelling each way. If it's a two week trip, pay a bit more for the shortest total flight duration. You could fly to Perth, but when you get there, you are in Perth....
The long haul budget airlines have methods to reduce cost - don't expect even basic economy equivalent from e.g South China. It will be fine in as much as you will get there. It will probably not be fun.
Not flying out of London is cheaper (and can be less busy). Looks like MCR will be a reasonable choice for you.
3-4 hr layovers are about right currently - depending on where you are transiting. Unless going in the pointy end, any less than that via the US is pretty risky. Look on Google Flights and then book via a travel agent, as that means they have to sort out flights for you in the event of misses/cancellations etc, and they are usually pretty competitive especially if you go in with a flight already researched.
Also - travel insurance.
Have a great trip. It's a heck of a country, the West Island of New Zealand.
b