Okay, you must buy a step because once you do your first Cathe workout, you will never get enough! Cathe does not have many hi/lo workouts. The only cardio, besides step, is the kickboxing already mentioned. Cardio Kicks is also a wonderful kickboxing workout. One of her older workouts, Maximum Intenstiy Cardio is 30 mins of step/30 mins of hi/lo. This workout is a very good intro to Cathe's workouts.
Do you have a high step or a "fanny lifter" that the Firm uses?