You are neglecting capital costs and Maintenance of Way costs and taxes.
Plus the costs of railroad workers and their managements.
I did mention that the trucks have the advantage of not paying for the roads they use while the monorail needs to be built at a capital cost of $2.5B. Divide that $2.5B by all the freight moved over a 50 year lifespan and it is only $50M per year. How many loads a year will travel on that 250 mile leg ? A million ? Ten million ?
Maintenance of roads is included in the fuel tax rather than paid by the individual trucking companies (although there is also the mileage and weight portion of the vehicle tax on big trucks).
Maintenance of the monorail would have to be paid by the operator — presumably out of their 92% operating cost savings compared to trucks.