Average calories burned: 800
Cost per class: $30-$40, depending on location
Cost per calorie: 3.8 to 5 cents
Class time: 1 hour

Barry's Boot Camp alternates between intense treadmill action and weight training, so you get the best of both worlds -- you build muscles while you burn calories. The low lights and rows of treadmills may seem intimidating at first (especially if you don't consider yourself a runner), but a glance around the room at the superfit people will show you that something, clearly, is working.

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Average calories burned: 660
Cost per class: $26
Cost per calorie: 3.9 cents
Class time: 30 minutes

A favorite among celebs like Emma Stone and Ashley Greene, this boutique climbing studio boasts a 30-minute workout that burns calories and tones muscles. (Seriously, if you want a killer upper body this is the place to go.) The lights are low, and the music is loud and pulsing, keeping you motivated as you climb to the beat. Since this slightly-tortuous-but-worth-it class combines cardio with muscle building, you'll continue to burn calories long after the workout is over.

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Average calories burned: 500
Cost per class: $16
Cost per calorie: 3.2 cents
Class time: 1 hour

A combo of Pilates, kickboxing and dance, this class packs a fat-torching punch while toning your muscles. Translation: You get the lean-muscle-building benefits of Pilates and boxing -- not to mention the abs workout of both -- plus, the cardio burn of high intensity intervals. A note: If you don't like to dance (in public, anyway), you may want to skip this. There are definitely some Zumba-esque moments.