I just went to Grace Bros/Myer and bought a copy of the DVD for 16 dollars that had both the Director's Cut and the normal version on the one disk - there were quite a few copies too. I just reccomend going to the nearest large shopping centre and looking around, and if you cant see it on the shelf - order it in.
You've already completed your HSC (unless you're stuck in Groundhog Day) but for anyone else that wants to know, I bought a copy of The Big Sleep on DVD at Dick Smith Powerhouse at Macqaurie. I did take the last copy, but i don't see why they wouldn't restock. Mine was 22 bucks i think, which might be a little to expensive on my budget, but its worth it if you want to pause and take notes and watch whenever you want.