And I've found the definition of "cost-sharing":
a flight is a cost-sharing flight if:
(a) the flight is conducted using an aircraft with a maximum seat configuration of not more than 6, including the pilot’s seat; and
(b) the pilot in command is not remunerated for the flight; and
(c) the pilot in command pays an amount of the direct costs of the flight that is at least equal to the amount that would be paid by each person if the direct costs were evenly divided between all persons on board; and
(d) the flight is not advertised to the general public.
Example 1: For paragraph I, if the direct costs of a flight are $3,000 and the flight has 5 persons on board, including the pilot, the pilot must pay at least $600 towards the direct costs.
Example 2: For paragraph (d):
(a) an advertisement in a daily national newspaper is an advertisement to the general public; and
(b) an advertisement in a flying club newsletter is not an advertisement to the general public.
Hmmm, so the pilot can be rewarded but not remunerated. That's inconsistent with the passage lumps quoted from the CASA document.
And whom does the PIC have to pay?
Let's assume the registered owner and operator of the aircraft is ABC Pty Ltd. ABC Pty Ltd hires the aircraft to the PIC at $X per hour wet. The PIC and four mates go on a flight and ABC Pty Ltd charges the PIC $3,000. The PIC chips in $600 and his mates come up with the balance and that's paid to ABC Pty Ltd. Does that satisfy the definition?