Look into explorer fares (used to be walkabout pass) with quantas. You’ll get cheaper domestic fares on multi city stops as long as you fly with them from the US (or wherever you’re from). That way you can hop from city to city. Some of our favorites are on the southern coast- Kangaroo Island, Great Ocean Road, and the Grampians (inland). Uluru was a great stop just to say you’ve been there and GBR is fantastic (Fitzroy Island is popular with a lot of people who don’t want to break the bank but want to stay close to the GBR- you can take a boat out for diving/snorkeling at the reef from there).