Last I checked a land based 208 was $850 to $1000 per hour on charter with a pilot.
An amphib would be more, I'd guess at least 25% for freshwater ops.
Sounds like that Cessna number is fuel\MX (estimated\ and engine allowance.
Again amphib ops will increase that number.
As your pilot is pretty cheap you could figure that the difference between direct and charter cost is being mostly absorbed by capital costs, depreciation and insurance.
20driver