This article[1] suggests excise tax isn't that high ($1 or $2), though GST is 10% so that's certainly part of the overall price.

I rather suspect it is pure price discrimination. I saw Pabst Blue Ribbon for AU$49 a case. PBR! Sierra Nevada Pale Ale is around AU$75 a case. These prices are at a huge discount retailer (Dan Murphy's).

[1] http://theconversation.edu.au/calling-time-on-alcohol-taxati...