There are support costs for media. You can call a dealer or the manufacturer and ask for information, help with profiles, driver settings, stock QA, asssitance with selection of appropriate media, pretty much order any of the available sizes on demand as it's all held in stock for you so on and so forth. Of course, these compaines (the dealers and the vendors) don't just sell media. They have other costs. Those costs are spread among the various products and services that they sell. They will choose a business model that is profitable (which means one acceptable to the market, among other things).
They are senstive to feedback - if the market isn't buying, they either change their price, their delivery or their product (they might also engage in discounts, advertising and so on). If the market is buying, they are less likely to make changes.
The entire world is not the same. It costs different amounts to conduct business in different countries. If, for example, the advantages of the US market were spread across the rest of the markets to bring the prices down, it's possible that the profitability of the US operation might decline and require higher prices to sustain it. This may make it unprofitable in that market and thereby remove the capacity to support other operations in the first place.
This is just one of literally dozens of examples and reasons why pricing varies. Numerous others have been provided by a number of people. Ultimately, though, everyone agrees that if you don't think it's good value then don't buy it and tell the vendor why.
Or, do you really think that every vendor and dealer selling media in Australia are all working together? Canon, HP, Epson, Canson, Hahnemühle, Innova etc, etc all working together to conspire against the Australian market?
Let me ask you - how much do you sell a print for? What percentage of that price is the media? If someone in the US can deliver a print of equal quality and similar subject for a signicantly lower price are you price gouging? No you're not - because price gouging is where you take unreasonable advantage of a shortage of supply due to unusual circumstances (say a natural disaster) to charge a price significantly inflated above the normal price in THAT market.
If you can deliver a lower price to the US than a US vendor but the freight costs so much as to negate that advantage, is that your fault? Of couorse not.
If you supply through a reseller rather than direct and you have a deal with one in Australia and one in the US and you tell them not to ship to the other region because you already have an appointed distributor, are you doing anything other than normal business management of a distribution channel? Is there some law that says you must sell to everyone and anyone anywhere in the world directly? Certainly not.
Again, Sven, this is why I usually don't join in :-)