Unfortunately the Sydney-Ayers Rock is one of the more expensive routes due to Qantas having a monopoly on it. The cheapest listed at the moment is about AU$600 return (or US$400 or so). You could go to Alice Springs instead for AU$400 return, though it's still a fair drive from there to get to Ayers Rock - depends how much driving through the desert appeals to you I guess. There's usually decent award availability out there though, especially mid-week, so could be a good option to take a look at.