Julie Bishop must Go!, page-31

"Every cost is already sunk though, apart from the fuel."

Not true.

You need to understand the difference between a budget and expenditure.

A budget is a provision for intended expenditure, it does not become an expenditure until the money is spent. That is why we have either a surplus (i.e. spent less than budgeted for) or a deficit (spending exceeding what has been provided for).