Wanted: 15 to 25 Horsepower Long Shaft Out Board

I am looking to spend between FREE and $750. I want this engine to throw on my drift boat (1991 Willie 16 x 54) for fishing the Sound and maybe places like the Cowlitz. I have seen some others with the same set up and they seem to get around really well. For what I want to do this would save me from asking my wife to let me get a whole another boat. If you think this is stupid let me know as I am always open to whether something is just a bad idea. Thanks, Nick

Oh...I am looking for one in good working condition.