I just ordered a non-mint Crypt of the Everflame as an experiment. I also added in Giants Revisited to fill a gap in my collection.
The US-UK postage was just over $6. By being a subscriber, I get discount on the two items of just over $6. (US Dollar rates)
The solution I can see is buy the core rulebook from Amazon and pay the $40-odd (no idea if this is USD or AUD in your example) and then order Crypt from Paizo. You should pay a similar rate to what I do in postage - I run an internet retail business and it costs me exactly the same to post an item to you in Australia as it would to send it to someone at Paizo on the West Coast of the US from where I am. If I was to send you a mug, say, weighing 400g (just under 1 pound, US posters) it would cost me £6.60 to both destinations.
The Core Rulebook weighs a ton though - that is what is hammering the postage for you.