I don't think Sydney is known for its diving......
:no where is my slap-down smilie!!!
sydney has dozens of dive sites avaible plus most of them are shore dives so it doesnt have to be as expensive as boat dives but the trick is to make a list of things you want to see and dive those sites
eg:
grey nurse shark = boat dive/magic point at marubra (shiprock dive or scubaroos or prodive does this site)
weedy sea dragons = kurnell shore dive
seahorses = manly or balmoral nets
angler fish, pipefish/muck dive = clifton gardens shore dive
a bit of everything = bare island shore dive
and these are just a couple of our dive sites
then you can go 2hrs north to nelson bay or south to shellharbour for excellent diving also
my recommendation is Kurnell for the weedy sea dragons - reason is you wont find them anywhere else in the world but here in australia. Abyss Scuba should be able to help you out with this
you do get the weedies at Bare Island also but kurnell is more a guarantee
cheers