I've heard of it, and yes, it's a classic in the genre of shooter games. I doubt you can get a copy of it for $40 Australian, however, you can get it on ebay for around 50-60 US dollars. Or you might get lucky, but all in all, the game is now a collectors' item and add that to its original rarity, it'll be very hard to find anything under $50. Oh, and might I add... the game itself is exceptionally difficult.
EDIT: oh yes, and I forgot.. if you're in Aus, it'll be even harder to get, because a lot of ebay sellers won't ship to places outside of the United States.