Blizzard Store - World of Warcraft Battlechest OR Expansion Packs US$10 Each (also ships to Oz)
Only $10 for the battlechest (2 expansions) and $10 each for the other expansions.
If you want to play the game from scratch, it will cost US$30 and you also receive a free 30 day game play with it.
Good price to pay to test out the game :)
Usually, they are about $35 for the latest expansion pack, and $20 each for the older ones. So you will save a chunk.
They also ship out the physical game, and testing it.. it costs $27+ to ship 3 games/expansion packs to Australia, and cheaper if you ship more. On eBay, the latest expansion pack-Cataclysm is selling for $35ish + postage.
"For the Alliance!"
ps Sorry showing the geek in me..I did use to play this game in the past ;D