I know the disney resorts will have buses leaving from each of the Disney resorts to the expo about every 30-45 minutes (but I don't know if this includes S/D) I would ask at the desk. Also, note that the marathon buses don't always stop at the regular bus stops at the resort. You could drive, but I did for the 2005 race, and thought the traffic was horrible--of course, since you're going on Saturday, that would be less traffic since it would only be for the marathon pick up.
It is my understanding that there is a bus that runs from MGM to WWOS>