I have bought some of these and it costs $7.15 to send items in 500g ebay satchels vs $8.25 in prepaid ones. For the larger bags up to 3kgs it is $11.70 for ebay satchels vs $13.40 for prepaid. This is on top of the the 20c or so for each bag.
After getting the bags you sign up to
https://www.clickandsend.com.au/home/NISS_frm_home.php?sz_Client=AustraliaPost and pay for postage through the site, then print out the address label for the the bag.
It sounds like a lot of trouble but is better than getting to a post office before it closes and cheaper too.
