trapper,
According to my handheld gps, the 51lb trolling motor pushed it at a little over 2mph and the 2hp a little over 4. With your legs out in front of you, using the flippers for a rudder, that's fast enough for me.
7lb,
You just have to find someone who has one lying around. They quit making these several years ago. Mr Sir, here on TFF, sells a styrofoam kick boat, but I'm not sure it will handle a motor. You might check with him. I've seen homemade from styrofoam that have been beefed up by coating it with fiberglass and then adding a transom for a motor.