Lethal Weapon 1-4 boxset now at the lowest price (I think) ever at Amazon UK.
£12.99 with VAT removed is £10.83 (VAT is removed at the last checkout page), which is roughly AUD $16.50 (according to Google).
Doesn't qualify for free shipping by itself since it's not over £25, but you can add a few more items to get it over the limit, and there are quite a few "lowest price ever" titles around, including:
Scott Pilgrim / Hot Fuzz / Shaun of the Dead [Blu-ray] ~AUD $17
Jurassic Park Ultimate Trilogy: Limited Collectors Edition [Blu-ray] ~AUD $35.50 (I've posted this before, but it's back in stock again)
True Blood Season 1-3 [Blu-ray] ~AUD $50.60
The Complete Matrix Trilogy [Blu-ray] ~AUD $19.12 (thanks Steptoe)
X-Men Quadrilogy [Blu-ray] ~AUD $12.75 (thanks couger)
All UK Blu-ray's carry the same region code as Australia (region B), so they should all work on Australian Blu-ray players.