Just wanted to add, that I think one of the major factors is so called "Free Postage" & the expensive postal costs of Australia Post.

If an item is worth $7.00, and weighs over 500 grams, then add the postage cost of approx $13+, therefore the price to purchase has to be $20.00.

No such thing as free postage for anyone. 

Needs to be called "Price Includes Postage Costs" .  (says me again)