Traveling to South America is always expensive, coupled with over holiday / peak travel times, you are unlikely to find anything that's much better than 2K pp vv.
The obvious one is look at what day you are planning on flying out on, sometimes an extra day / one less day can cut the price in half (or double the price), the other one is look at points you have / can get, whilst Y does typically represent bad value for points redemption, I myself have used a Y classic award to do a trip which I would not have otherwise been able to afford.
Look at non AU sites to see if you can get a better deal.
Look at your routing and if there are any south american flights you'd like to do at the same time / see if flying via North America is an option. Since here to the US return is only around $1K pp vv, that would still give you up to $1K pp vv to get from North America down to South America (a friend of mine did a similar thing a few years back). Compare all airlines and all options, since it might be that VA SYD-LAX but LA from LAX to EZE gives the best value, despite not being aligned.
Also whilst it might not represent a saving on the AU-South America fare itself, something like a circle pacific might be able to let you throw in additional destinations which you where planning on traveling to anyway for roughly the same cost. If you where planning on flying in South America it could represent a saving there.
Just some food for thought...
