Free return flights on Jetstar.
Natgional and International flights
I have used this before Wellington - Gold Coast return for $149 (it appears all the return flights this time are via Auckland)
How to find and book your Return for FREE^ flights:
Click the ‘Find Flights’ link next to your preferred flight, or search for the flight you want.
Make sure you select a ‘return’ booking.
Select your first flight on any travel date.
For your return flight, search for flights within the available Travel Periods, listed below. Not all destinations have the same Travel Periods, so be sure to review your chosen destination carefully to save time.
Enter the number of passengers you’d like to book for and click ‘Continue’.
Look for a return flight labelled ‘$0’ (may not be available on all flights or days).