I too am in Newy. Currently building an MDF CNC (see build thread link below). Using skate bearings for X & Y axis and linear bearings for the Z axis. Got my skate bearings from VXB.com (US), 50 bearings in total for $58 US including shipping. The linear bearings and shafts I got from the same ebay mob you've looked at. Product seems good (for price....) and prompt service, although they haven't been given a work-out yet!
I priced some 8020 al (25-5010, 50mm x 100mm T-slot) from http://www.8020.com.au/ (Seven Hills, Sydney) and the quote came back at $320 for a 4metre length! Unfortunately not in my budget! Haven't investigated if it's available anywhere else in Aus.
This forum has a wealth of information, it just takes time to find it......! Try also http://www.woodworkforums.com for Aussie built metal and timber DIY CNC.
Good luck mate. Keep an eye on this forum, there is possibly going to be a get togethor bbq for interested Newcastle people soon.