The more people you have, the cheaper it is to drive. If it was just one person, a plane ticket and shuttle would probably work out to what the gas and parking will cost. Add more people, and the gas and parking don't go up, but the plane tickets do.
Does your hotel charge for daily parking? Will you want a car while you are there? What do the airlines want for Oct (I know in June it's only about $49 each way on USAirways)? Factor accordingly.
Flying doesn't save as much time anymore since you have to get to the airport super-early and go through security. I find by the time I leave home (East Valley), drive to Sky Harbor, park, shuttle, security line, wait, fly, shuttle, etc., it only knocks about an hour or two off of what it would take to drive to So Cal!
We almost always drive because we drive with several people. I've only flown when I was by myself and had a ride waiting at the other end.
PHXscuba