Brother, I share your weakness for oysters...
If you are willing to have a go at shucking your own oysters, it is cheaper to buy them unopened. Shucking oysters is not hard at all. First few are tricky until you figure out the knack
Many fish shops offer bags by the dozens this way, much cheaper than shucked. I stuffed myself with 40 oysters this way in Batemans Bay a few years back. Bag of oysters was a bargain, a shucking knife costs bugger all and lasts just about a lifetime - I still have the knife I bought then, and gets used regularly
And the flavour of those oysters you shuck, without being rinsed in freshwater, oh me, oh my...
Another way to do this is shucking oysters along the shoreline. Not necessarily something you would want to do too much of in Sydney Harbour anywhere west of Rose Bay, but fine along the other oyster growing estuaries.
It all then comes down to where you would like to go where oysters are farmed. The Oz coastline has many, MANY fine oyster fisheries! This also opens a lot more accommodation options.
Alex.