Australia post is able to provide overnight express postage upto 3kg in weight for approx $9.90 inc GST. This service covers most of Australia but some remote places arn't covered. If you are in a remote part of Australia then faster than normal delivery will be provided. Express post can used for larger parcels but is very expensive.
Standard parcel post:
Takes a day or two longer than express but is very affordable. It costs about $5.00 per parcel + $0.55 per kilo inc GST to Melbourne.