May I ask why you don't want public transportation? You're going to be two miles from Union Station, you can take a cab from Santee to the train and it is a straight shot to Anaheim, where you can get another cab to wherever you need to be
Disneyland or a hotel or ?
The thing is, the train is faster than traffic, especially if you are going during lunch or rush hours. I've taken the train from Burbank to Anaheim many times just to beat traffic.