Fuel is definitely more than half of the operating costs of my car, the way I run it. In any case, I was not really interested in the operating costs of my car for the trip from Launceston to Lake St Clair, I was merely using the cost of the fuel to get there to explain how much money I had to have "in my pocket" (so to speak) to get from home to the start of a bushwalk, and that catching the ferry MORE than doubled the cost of the round trip from that perspective.
I'm not disagreeing with you, though. They may well have good sound reasonable business reasons for charging that much, but unfortunately, it does make many popular bushwalks unaffordable for a large number of people.
It's also worth noting that they have a minimum charge per trip when there are not large numbers. I think when I did it in winter many years ago, they wouldn't go unless you had at least four people (or paid for four people). Most staff who have seasonal work find other jobs in the off season too, so staff costs are much reduced in the off season (I don't know how many staff they have, and if this really makes any significant difference to this particular business, or not).
They don't have a monopoly on all transport between Cynthia Bay and Narcisuss, but they certainly do have a monopoly on passenger ferry services between those two locations. Yes, there is the option of walking (which I already choose over the ferry when I have the time), but walking is simply not an option for many trips - eg, those who want to go into Pine Valley for the weekend, or a number of other locations for short trips.
So I'm not criticising them for charging what they do (I can't say one way or another if they're "doing the right thing" or not), but I'm merely stating that the massive increase in prices of this ferry service over the last 10 years or so has made some bushwalks unaffordable and impracticle for many people. 10 years ago, I would drive down there at the drop of a hat and wouldn't think twice about paying the small charge for the ferry (despite the sometimes grumpy disposition of the staff at the time

), but these days, I cannot afford that, which means that I need to add at least 1 day to most of my walks in that area, which means that I cannot do them merely on weekends, which means that I've got to take annual leave to do those walks.
So it's not a good thing for bushwalkers, the way I see it. However, it may well be required to keep the business afloat (and so long as the service survives, then that is a good thing for bushwalkers).