(Read here: http://mishellesleepytime.blogspot.com.au/2012/10/makeup-mark-up-usa-vs-australia.html)
Whenever I want to buy something, I work out how much I'd save by buying it online from a US store and having it parcel forwarded to me. Parcel forwarding is also good for getting products that you can't get here in Australia like Urban Decay.
I use the company PriceUSA which is run by Carolina in Melbourne and her US partners in Oregon. I've used them a number of times and as a disclaimer: they haven't asked me to write this review about them. I was requested to do this post by Sophie from http://dontstopbuying.blogspot.com.au.
How it works is that I'll fill out the order form on their website, letting them know what I want and where to order it from. Shortly afterwards, Carolina will email me a quote of how much she estimates my order will cost and if I want to go ahead, I pay a deposit into one of the PriceUSA trust bank accounts.
One of Carolina's US partners will then purchase the products and ship it to themselves. When they receive the order, I get emailed a final quote and I pay the rest of the balance before they ship it out to me. My estimates have generally been spot on or $1-3 short.
I save a lot of money by using PriceUSA as my parcel forwarding company (they don't charge fees unless you use Paypal or a credit card to pay them). As an example, I recently ordered 5 MAC items from the US and saved almost 50%.
I hope that helps! If I've been a bit ambiguous, let me know and I'll try my best to explain it a bit better.