Even if manned by reservists (which we do not have with the required commercial tickets in the necessary numbers) the crew will still be on Australian conditions ........ and that is not cheap.
The UK's sponsored reservists are not ex-service members. They are commercial sailors who agree to become reservists.
I think that the point is being missed about the costs. The purpose of chartering the ships is not to make a profit, but reduce the cost of ownership. A commercial operator has to cover fixed costs: chartering out an underused military asset can be worthwhile as long as it covers the marginal costs.
Chartering is limited by the need to be able to withdraw the ship on short notice in an emergency (
NOT on a whim), & that may affect the price of charters as well as those which are available, but it has worked for the UK.
I don't think anyone would consider that a chartering operation based on the spare capacity of military assets is a sound commercial proposition if it has to compete with standard commercial operators on the same terms, but it's been shown to be able to reduce the cost of ownership for the military - because it doesn't have to compete on the same terms to do that.