All right, I just did some math here. In US dollars, the cost of Tally-Ho decks (half-dozen of each variety) is $2.02 a pack or $24.24 a dozen from Theory11 - the cheapest prices I've seen for them at retail. Each deck weighs approximately 3.3 ounces, so the lot would weigh about 2.5 pounds.
The cheapest international method of shipping T11 offers is US Postal Service Priority Mail International. If your delivery would fit in a Small Flat Rate box, it would only cost $13.95 - BUT using standard measures for a deck of cards (approx. 3.5" long, 2.5" wide, 0.7" thick), a brick won't fit, especially when inserting packing material. If, however, you ordered maybe eight decks, it would fit in the small flat-rate box (snugly, but it would fit with packing), and you wouldn't get raked over the coals on shipping. You might actually get away with making an eight deck purchase for as little as US$40-$45. Current exchange rates have the Aussie dollar nearly identical in value to the US dollar.
The small flat-rate box is in inches 8-5/8 by 5-3/8 by 1-5/8. Max capacity 4 pounds.
The alternative is the medium rate box, max cap 20 pounds. Measures either 13-5/8" x 11-7/8" x 3-3/8" or 11" x 8-1/2" x 5-1/2" (two sizes available). The cost is a murderous $45.50.
There are slight discounts for ordering postage online, but not enough to make a huge dent in the cost, plus T11 will charge you enough for packing to make up for those savings and a little more.
Best possible solution for you is either:
1) Save your Aussie dollars and place a BIG order to make shipping worthwhile, or
2) Place an order 1/3 less and get reasonable shipping. Specify to T11 to use small flat rate box if possible to save on costs, though they're likely to do that anyway. Ask if they'll still give you the six-deck discount of 10% percent if your six-or-more decks is split between two varieties of Tally Hos. Otherwise, you'll only get 5% off the normal $2.25 price.
I wish I could tell you that Tally Ho was cheaper/easier to get. USPC considers it a regional brand, and the geographical region in question is now just the New York City metropolitan area (I live there). They're not easy to find outside of New York except for magic retailers both online and off, so it makes it especially hard to find internationally. Major national retailers here are only interested in nationally known brands, or at the least a regional brand with a larger region than just one metropolitan area. It's a shame, too, since they're among the finest standard cards USPC makes, and were even requested by name by a character in the classic movie "The Sting".
Consider getting together with friends and placing a larger order, or ordering from wholesaler Kardwell or perhaps even USPC if they'll allow it. Be leery about ordering from Asian companies - there's been a lot of counterfeit USPC product coming out of East Asia, China in particular. I helped them track down a distributor of the bogus goods recently. I just checked Kardwell and you can get a mixed half-gross for $147, discounts for full and two gross orders.