When you give any service company- boat, car, outboard, etc a cart blanche authority to "do the annual service" you get this sort of thing, but it does sound exorbitant.
An annual service should include an oil and filter change, a lower end top off or change and not much else. I did these on my Yamaha in about an hour and $20 in oil and parts.
The manufacturer also includes a lot of check/replace items in their recommended service. How do you check an impeller or the thermostat without running the engine for a while? So some might just replace these items.
So there is a lot of interpretation required and it is easy for the service guy to run up the bill while following the letter of the manufacturer's recommendations.
Next time specify exactly what you want changed and what you want just looked at.
FWIW car dealers have gotten much better about this sort of thing. My Nissan dealer typically charges half of what you paid for an annual service and oil change and over the years, recall service (free to the customer) has resulted in much more business than the annual service charges.
David