I don't think that high speed is what he needs so the power requirements wouldn't be all that bad. Where he looking at a sailplane type of design with a 14 ft span I don't think size is all that much of an issue either.
Your right a hybrid blimp/airplane would be fairly large, but you have both the gas and aerodynamically generated lift working for you.
But all in all the sailplane approach my be the easiest.
I'm just throwing out some food for thought...