It's a bit difficult to give an overall figure, the last time I went to Australia I was there for just over a month and the trip for a friend and I cost almost 4000pounds each. You can of course do it much cheaper than that or spend a lot more. Accomodation prices vary immensely and unless you really want four star hotels then two and three star are usually OK or as I believe you are in your 20's backpacker hostels may suffice.
There are lots of variations of itineraries do you want stop overs? it's two long flights each way and I always like a break, you may not need one but if you do it will add days and expense onto the journey.
Most stopovers are in either Dubai, Singapore, Bangkok, Hong Kong or Kuala Lumpur depending on the airlines chosen.
Do you also want to see West Australia if so a suggested itinerary would be Perth maybe 4 nights, fly to Sydney again 4 nights.You may want to miss out Perth and fly directly to Sydney and spend more days in both Melbourne and Sydney. Fly to Melbourne from Sydney for 2or 3 nights, hire a car or take a 3 night tour down the Great Ocean Road to Adelaide visiting Kangaroo Island on the way , fly to Alice Springs , take a 4 night tour to Uluru visiting Kings Canyon on the way, or just fly directly to Uluru, fly to Cairns and have 4- 5 nights there, visit the Great Barrier Reef and have some relaxing time as you will definitely need it by then.
Read some of the posts on HT by people who have visited Australia or look in some guide books or brochures for ideas. Travel firms such as Travel Bag are very good at arranging individual holidays and will give you a quote if you tell them your needs.
Don't try to see everything (not possible in 4 weeks anyhow) Australia is a very large country and distances are huge. Apart from the journey down the great ocean road I wouldn't advise driving. Fly everywhere there are a number of low cost airlines. I'm sure the you will get more advice from people who have travelled to Australia and I expect our resident Aussie Chubby will have some tips for you. Have a fabulous holiday it's a great destination, I've been twice but I'm still wanting to return to see more of the country.

Can't give you an idea on prices as it's a long time since we did it, but would also suggest trying Travelbag or Trailfinders. We used a local travel agent when we went.

We went for a month and the flights were with Qantas. I didn't think much of them and would choose another airline if I was doing it again. Cathay Pacific looked good, but obviously it comes down to price. Our flight price included 3 internal flights.

We did a stopover in Hong Kong on the way out and stayed there for 5 days then flew to Brisbane and stayed with people we had met on holiday for 9 days in Ballina. While we were there we went to Surfer's Paradise, the Gold Coast, Lennox Head, Byron Bay, etc.

We then flew to Sydney for I think it was 2 nights, but could have stayed there longer so we could visit the Blue Mountains, etc. That said we packed a lot into the 2 days we were there. We went to a musical at the Opera House, went on the ferry to Manly, did an afternoon tea cruise on the Bounty, visited the Rocks and the Victoria Buildings, went on the monorail, went to Darling Harbour, etc.

We then flew to Ayres Rock via Alice Springs and had 2 nights there and hired a car. We were able to visit Uluru and the Olgas. Flew to Cairns and stayed at Cairns Colonial Club which was very nice. We went up to Kuranda on the scenic train and went diving on the Great Barrier Reef from Port Douglas.

We had a stopover in Singapore on the way home for 3 days.

It was a great trip. I think you could save a fair bit if you DIY'd it rather than doing an organised tour. ATT Kings rings a bell so you could maybe look them up as that should give you an idea of a tour price.

luci

Its AAT Kings Luci. I used them for a four day tour from Alice Springs to Uluru stopping off at Kings Canyon on the way back to Alice Springs. APT are another well known Australian tour company, I used them for a five days of touring of Kakadu, Litchfield and Catherine Gorge from Darwin both were really well organised but not cheap. One good thing is that they do offer different levels of accomodation.

Judith