You don’t need to have a return flight booked on a working holiday visa. If you do not have a return flight booked, you will need to show an additional $1000 in proof of funds to demonstrate that you will be able to purchase your flight home when the time comes. However, you do need to have a return flight booked if you plan to arrive on a visitor visa, so make sure to tell any friends or family who would like to come to visit for a week or two once you settle in.