Did you know that you need to have proof of funds of AU$5000 when you enter Australia on a WHV? Even if you didn't, the best plan before leaving for Antipodean shores is to save, save, save for your trip - and here's a few useful sites for saving money when booking your flight.
The website I have used the most when booking international travel is called Last Minute - the clue’s in the name; often if you book close to your travel date, you get a cheaper deal. I used this website for both of the first two times that I flew to Australia, and managed to book return flights from London Heathrow to Brisbane for £615 and £650 respectively, instead of, say £850 as advertised on the airline websites. So you get an idea, I booked my flight around one month (in one case, 3 weeks) before flying, but was still able to get these prices with Last Minute.
This trip in June will be my third to Australia, and once again I booked with Last Minute after double-checking the prices on offer at the major airline websites. This time I'm stopping over in Hong Kong, so I booked to depart the UK on the 29th of May, and depart Hong Kong on the 6th of June. My first flight is with British Airways, and my second with Qantas (both economy of course)... and guess how much my two flights with a week-long stopover cost me? The grand sum of £632 - that's not much more than an individual return flight to HK!
[Side note: Last Minute books flights with all major international flight companies (British Airways, Qantas, Singapore Airlines, Cathay Pacific, Air France, Emirates, to name a few), and a few lesser-known ones. I would advise doing your homework if you opt to fly with a lesser-known airline - my last flight to Australia in 2008 was with Royal Brunei, the state airline of Brunei. It was a ‘dry’ flight (no alcohol on board) and I knew that when I booked it - but some people may find that a horrifying prospect!]
STA Travel is an excellent site for travellers aged 26 and under - their business is based around providing lower-cost travel to younger people. They do a price-beat guarantee, and are also low-cost travel insurance providers.
You could also try checking with a price comparison site, such as Travel Supermarket - this is similar to Last Minute, where you get to review and compare a list of flights offered by different airlines, their full itineraries and costs.
I've also heard good things about Flight Centre, particularly from Australian travellers and bloggers (it's an Australian company). I don't have personal experience with it, but I'll definitely try it when booking domestic flights in Australia.
Remember that if you want to save money - and I'm talking potential big bucks here, £200 or even £300 - the worst thing you can do is to log onto a major airline's website, type in your dates, and buy whatever available flights they have. Don't be afraid to spend some time shopping around and comparing prices - it'll take you 10 or 15 minutes max - and remember that flight prices fluctuate according to days of the week (Tuesdays seems to be the lowest-cost days), so keep your dates flexible. Finally, always remember to stay safe while shopping online and stick to reputable service providers. Good luck!