Want to start kickboxing at LA Boxing. What's the workout like and is it good to stay fit?

im 15 years old and want to start kickboxing cause it looks like a fun way to stay in shape. im a gymnast and i need to stay in shape so i can start training again in a few months. i want to increase my arm strength, legs and abs. im already in good shape and have good flexibility. what's the kickboxing workout like there? all the ads and commercials they have say u can lose 800 to 1000 calories in an hour. is it expensive?