Wait a minute, you are going to be in Ketchikan for ONE day, and want to buy a boat for fishing that one day?
I would go to Knudsen Cove and rent a skiff for the day. That's all you need when the weather is good; when it isn't, you don't want to be out on the water anyway! Be sure to bring a camera with several SD cards. Again, if the weather is good you will be taking lots of photos.
-WH-