I say save the money. If you're comfortable telling stories about yourself and your experiences, be they true or not, your can prepare just fine in front of your own mirror.
I recommend going to aviationinterviews.com to see who's asking what questions lately and just practicing with the mirror, wife, friend, whatever.
On the other hand, if you're expecting a sim ride as part of your interview, some practice with a "standard profile" might help.