Hi Milly, how are you?
When are you leaving Australia? There's so much to see. Sydney is a beautiful city but it's in a world of its own. Sometimes I thought I could have been in any country in the world, apart from the sun and beaches.
I guess NZ is tempting to move on to but I'd a least go to Byron Bay while you are there; you could rent out surf boards for a week and camp on the beach. If you don't, you'll miss out on the surfer bum thing and all the other crazies that live in Byron. Also a trip to Nimbin, just next door, is essential.
Are you flying out of Sydney? Brisbane is just as easy. Money is a constraint but you could get a petrol share up the coast for $30...
Good luck with whatever you do,
Michael.