$100/month is pretty good if you're getting 1-on-1 or small group attention from a trainer each time you go. I work as a personal trainer right now and we charge around $5/hr for groups for 3-6 people for 3 months at a time. I end up doing crossfit style workouts with them anyway. Crossfit, P-90x, and insanity from a scientific standpoint are great for getting you into shape, but they are terrible for progression once you get into a routine for 6 months.