Second, you don't need special equipment to work your abs. You can do a wide variety of ab exercises with just your body weight or with an exercise ball, which is often much cheaper than the gadgets you see on infomercials. For ideas, browse through these ab workouts and you'll see that challenging your abs doesn't require much equipment.
Conclusion: you're better off buying equipment that has multiple uses. Ab machines only work the abs, but things like dumbbells, an exercise ball, resistance bands, etc. can be used to train your entire body.
