One week Sydney Yellow Travel Pass: All ferries along with buses and trains as far out as we would want to go - $50 plus possibly using the airport train, an extra approx $20 return.
Five day Sydney Pass: All ferries including River Cats, all Sydney buses, City Rail trains with the red zone, Hop on hop off Bondi and City Explorer buses, train from airport to City return, discounts at museums and other attractions - $150. We will be in Sydney for six nights and so probably won't need public transport the first and last days, the train part is not part of the five day period.
Tempting, but I am not sure. Maybe we will just pay as we go. Day tickets for trains, buses and ferries cost $17, a lot more than we would pay in Melbourne for a tram, bus and train daily ticket. Unfortunately, the Sydney tram and Monorail are not included in the day ticket. I can't imagine we will want a daily ticket every day though. Plus, it needs to be a relaxing holiday, not a race to make sure we get full value from periodical tickets.
I guess I need to plan out a bit more what we shall do in Sydney.