Sydney Airport TBus terminal transfer service between International (T1) and Domestic terminals (T2) is now FREE (as of about 2 weeks ago). Previously cost $6 each way. Wow freebie by Sydney Airports Corporation, who'd have thought?!
Photo is of the Tbus stop at International (not particularly well sign posted). You'll see the new complimentary sign sits above the now covered up defunct ticket vending machine.