I have 200 gallon tank as well. However I have about six 6 gallon gas cans that I take to the gas station and fill up. At $4 I would have to figure it is at least $5 on water.
Two weeks ago I talked to a guy that kept his boat at the Harborage. Gas was $4.66 a gallon and he said in the next week they were going to raise it to $5.66.