I use Fastways as much as possible for my 2 stores. Their A5 bag can hold up to 1kg and costs $6.40. They are faster than Express Post in most cases (not to opposite coasts and Tas). The only problem is that they do not deliver to all areas in Australia when using the Pre-Paid bags. You also have to fill out the registration form and pre-buy the bags (come in packs of 20)

All parcels (unless authorisation given) are signed for and signature shows on the online tracking.

Cheaper, faster, online signature = winner