It was $88/car and $11/trailer last year, and has been for years.
It does sound expensive, but the alternative could be a lot more so
...plus it officially grants you access to some amazing places and campsites i.e.: Somerset, Mutee Head, Vrilya Point etc...
You could also ring the Injinoo Community Council who run the ferry.
Have a great trip! I can't wait to go back up.
Cheers
Karen