I just checked ITASoftware, and best I'm seeing is about $1600 for about a one month stay. Which to Australia isn't bad.
Another thing which a friend of mine did about 7 years ago is to fly to Hawaii, and then Jetstar has direct flights to Sydney from there. Right now they're look like 359 there, and 489 back, baggage likely extra, so not exactly a deal right now. My friend was only going one way, but able to get a seat sale to Hawaii from eastern Canada for about $400, and then it was under $300 for the Sydney leg, and a free stopover in Hawaii. Just something to keep an eye on.
Having lived and travelled extensively in the SE Asia region, my go to strategy when coming from North America was to fly into a visa free hub (Singapore, KL, Tokyo, Jakarta) go through customs, then just catch a discounter flight to whereever. Unfortunately Australia, being so far from everything is a whole different beast. I'm seeing return flights to Singapore for about $1300, but then you still need to get to Australia, which will certainly cost more than $300...
The other thing I frequently do is to go to the wikipedia page for the airport (Sydney:
http://en.wikipedia.org/wiki/Sydney_Airport ) and it lists all the airlines and destinations. Check each one which connects in a hub you might be able to fly to for cheap from the US. I'm not sure what your idea of 'cheap' is, but if the stars line up sometimes you can save hundreds of dollars doing that.