If you are a stick stamps on the packages kind of person, watch for postage lots. You can often find them priced below face value, significantly below face value sometimes.
If you do a search on "australia face" amongst the items are a number of postage lots.
Note though that likely in Australia, same as here, it is probably illegal to reuse stamps so make sure they say full gum, MNH or if they are self adhesive they are unused on original backing.