Used 1950s-60s Evinrude/Johnson Lightwin 3 HP outboard. 2 cylinder. Water cooled. 2 stroke so you do mix gas. Self contained 1/3 gallon tank that will troll for almost a full day. 35 lbs. but built like a tank. Easy to maintain. Lots of new as well as used parts still available. Dependable and purrs like a kitten! Great for canoes and small (<14 ft.) boats on smaller bodies of water.
Many are still around, especially in the midwest, and many are still in nice shape. I've paid between $50 and $250 for the ones that I have had. My Grandfather's 1954 Evinrude still gets a lot of trolling use every year! Find you a nice olive drab "Ducktwin" and you will really have a nice piece. Those can bring as high as $1000 now for a nice restored one.