How does shore diving work there? Is it a guide from a local shop?
Where will you be staying, CBD, north or south of Sydney?
As justinthedeeps said, you will need transport to get to the sites as most shops won't provide transport for shore dives, you may be able to hitch a lift with another diver though but I would suggest talking to the dive shop first as they might be able to tee something up before hand.
The closest dive sites to the CBD are about 30 minutes by car, not including a visit to a dive shop.
You have several choices for dive shops, a few to look at are:
North of the city:
- Dive Centre Manly
- Frog Dive
- PRO DIVE Brookvale
East of the city:
- Dive Bondi
South of the city:
- Abyss Dive
- PRO DIVE Alexandria
Abyss Dive and Frog Dive do free shore dives (excluding gear rental) where other charge, this typically includes one or two DM's depending on group size and I know the Abyss one includes a basic lunch between dives.
Basically the way it works is that you turn up to the shop, sign a waiver saying if you die you wont sue, meet the guide/s, organise any gear you need and then head to the dive site that has been selected on conditions.
You can also pay to have private DM to take you out
Some of the shore dive sites are:
North:
- Shelly Beach/Cabbage Tree Bay
- Fairlight
Close to the city:
- Chowder Bay
- Camp Cove
- Shark Point
- Gordon's Bay
South of the city:
- Bare Island
- Kurnell - 3 sites: Steps, Leap and Monument sites
- Ship Rock
- Oak Park
There's plenty more, for a good resource on Sydney's sites, have a look at Michael McFadyen website:
Michael McFadyen's Scuba Diving Web Site
The two shore sites I would recommend as a "must do" would be The Steps (Weedy Sea Dragons, Angler Fish and Sea Horses) or Shelly Beach/Cabbage Tree Bay (Weedy Sea Dragons, Large Cuttle Fish, Turtles, large Groupers)
Be warned, the Steps is appropriately named.