Don't be fooled by the great sounding Oz weather. I was in Sydney from mid-Nov to early Dec and the weather was utter cr*p. I had hoped to do some flying, but there was no way - high winds, club base at 1000 ft agl, and heavy rain, for a good portion of the time I was there.
The flight is a bit of a killer - 22 hrs, plus stopover time. Unfortunately, this time of year is the most expensive time to go to OZ, with deals up over £1000 for economy (and that's not full fare).
Oz is cheaper sounding at the moment since the £ is quite good against the Aus$.
Time for your money must be South Africa. 5 star hotels for £30 a night and car rentals for about £10 for a weekend in Cape Town. The time difference is the same as for mainland Europe, and flights are much cheaper than for the US or QZ - but you've got to watch yourself.