Good luck with that! It takes money to make money.
There are many ferries across the US. Call Bullfrog marina in Utah and ask what they charge for their ferry.

First of all, the toll-"it has to be kinda small" will shoot this thing down for me at the get-go. This will take a lot of legal work, as it is crossing a national recreation area, which will involve the US Government, Utah and Wyoming.

You want to operate a ferry to cross Flaming Gorge Reservoir, between Jug Hollow Road and Lucerne Valley Recreational Road. Just how much traffic will you forecast there being?

You will need a diesel-powered ferry, 70 feet by 15 feet, with a 2 foot draft. This could be made on site if you had enough welders and permits to do it. You are probably looking at a cost of $150,000-$250,000. You will need a captain's license for this size boat from the US Coast Guard, plus all the safety equipment. I guess that you have plumbed the depths for clearance of the ferry. You will also need grading and bridging to get from the roads onto the ferry.

All in all, you will probably need about $500,000 or so, depending on how much lawyers cost and permits, etc., plus storage tank for fuel.

If you can carry 50 people a day, and rake in $500 a day, including the school buses, you can probably keep your head above water, if interest rates don't eat you alive.

If you can borrow $500,000, at 6% for 10 years, the monthly payment will be $5551.

Good luck, but I don't think that this is feasible. You might want to rethink this using a 20' pontoon boat, no cars or buses.
Maybe rent small john boats, or 15' outboards.

Regards,
Dan