Regs: Parking is expensive too - especially in city.
Last time I drove in Sydney (and it was a few years ago), parking was generally outrageous, true enough.
However, having said that, I found relatively cheap on-street parking (metered) in the Royal Botanic Garden, which is only a few minutes walk (and quite pleasant too!) to the Opera House and then onto Circular Quay.
A quick google search showed that you can get early bird parking (in by 9:30am, out between 3:30 and 7pm) at The Domain Car Park for $17, which isn't too bad (it's all relative!) http://www.domaincarpark.com.au/rates-a-times.html, so if you plan a bit in advance, you may find that easier / more flexible....
