Do you have any miles with AA or any Qantas partners? You might be able to do open jaw award travel on Qantas SYD-AYQ-CNS, and then buy a one way ticket on Virgin Blue CNS-SYD.

I priced SYD-AYQ-SYD ($A563 on Qantas) and SYD-CNS-SYD ($A279 on Virgin Blue) using Oct 4-7 travel dates just to get some fares, and that works out to about $US464, so this comes out pretty close to what you have with the airpass. I think the problem you're running into is that there is not any competition to Ayers Rock, so no reason to hold the fares down there.