Hi Zachery,
Businesses must state the total price as a single figure, which is the minimum total cost that is able to be calculated. This should include any tax, duty, fee, levy or other additional charges (e.g. GST or airport tax). If they are promoting a price that is only part of the total price, the total price must also be displayed at least as prominently. Customers must be able to identify the total price in the advertisement.
Failing to do this would be illegal under the ACL and may amount to misleading and deceptive conduct. Advertising an incorrect price to create a false impression is a breach of the Australian Consumer law.
I would either contact Subway directly and raise the issue with them, or alternatively contact your state Department of Fair Trading or the ACCC.