Getting your type...first very important step
Cost isn't everything and anyone considering getting the type should weigh the importance of who knows who and so on. But it ultimately comes down to your attitude, personality, and how well you show that you "fit" into the "Southwest" spirit during your interview, if you don't clam up that is. The interviewers all know that this is a huge deal for everyone and make you feel very comfortable so that they can get to know you, but you are on your way by getting the type for sure. All the applicants when I interviewed all had their types. Including the military guys.
For schools I would recommend Higher Power only because someone from the Southwest People department comes every Friday to personally talk to the class. It is an open session where you can have many of your questions answered, like "What are you looking for in an applicant?" and they'll tell you exactly what you have to show them! That has proven invaluable for me because the person who came to Higher Power that Friday when I was going through, just happened to be one of my interviewers!
Be prepared and practice your stories before you go for the interview, but getting the type is the first step. Make your own choices and remember that going the cheapest aint necessarily the way to go.