For s semi serious answer, I usually go through 5-6k for annual maintenance and upgrades. Some years more, some less, depending on the whim of the boating gods. That doesn't include fuel or insurance.
I saw a guideline somewhere once that you should plan annual costs at 10% of price of the boat, which I think included payments. Oh yes, for a used boat the payments go down, but the maintenance is still about the same % of the cost of the equivalent new one since none of the part costs scale with age.