For those that still buy physical media, Amazon have large reductions 74% off all the Star Trek Next Generation Blu-ray seasons.
All Next Generation seasons are US$31.99 (74% off), except for Season 1 (US$19.99, 74% off) and Season 3 (US$28.22 78% off), and except for season 7 which isn't reduced.
All TNG seasons are listed on Amazon.com as region locked to USA, but they are not. They are region A/B/C - ie all regions, according to Blu-ray.com reviews.
TNG Season 7 hasn't been released yet, but is on pre-order for release 2nd December 2014, and is not reduced in price.
Also found that the 'Original Series' (season 1-3) on Blu-ray is reduced by 79% to $68.89. This is confirmed to be region-free, according to http://www.blu-ray.com/movies/Star-Trek-The-Original-Series-...
Postage to AUS seems to be US$8.76 for the first item, then add US$2.39 per item thereafter. YMMV.