Courier companies are becoming more competitive, Fastway couriers, if you are prepared to buy in bulk offer national coverage 3 kg satchels A3 size for under $10, minumum purchase of 20 per month, includes insurance, delivery confirmation and they collect it, pretty good deal considering the cheapest Aust Post alternative with signature ebay satchel is $14.65. Here is their website link

http://www.fastway.com.au/pricing/courier-rates

just click on your city for prices. No I don't work for them, but I will be using them when my bulk purchase Aust Post satchels run out.

It's a question of what works for you, if you send a lot of items regularly then couriers are a way better option, as I said there are heaps of companies around, it won't be long before Aust Post have real competition and are forced to be more competitive. Remember Teltra and how awful they were before the market was deregulated, well some would say they are still awful but you get my drift, good luck x