When hiring from Brisbane City to the Airport, the drop fee is , ime, included in the total estimated price at time of booking
There is normally a drop fee between Brisbane Downtown and Brisbane Airport
I have just tried a dummy booking with no discount codes for a 1 day rental and a group C is pricing out on the site at $84.49 which includes the drop fee . When booking to return to Brisbane downtown the rate drops to $54.38
How much were you charged in total , what did the Rental Agreement say when you picked it up and what was the price quoted at booking time?
If the final invoice is different from the rental agreement, then I would give Hertz Customer services a call on 03 9698 2444 and they will sort it out within a few days