For those Aussie readers,
Mountain Equipment in Sydney has Lowe-Alpine Zepton 50 packs (featured in the 2010 State of the Market Report on Internal Frame Backpacks) for $150. Roger Caffin's rating for this pack was "recommended". They are indeed very light, and roomy enough for an UL bushwalker. Comfortable for me, too.
They're available in both regular and XL sizes at the shop on Kent St, their website has them for the same price but I can only see XL there.
Link to Roger's mini review: http://www.backpackinglight.com/cgi-bin/backpackinglight/lowe_alpine_nanon_lowe_alpine_zepton.html