What is a good teen workout and is affordable?

Running & Pushups: Running is a great, relatively cheap workout. All you really need to buy are some running shoes. Also, body weight workouts (i.e., calisthenics) are the cheapest workout, since all you need is yourself. These include planks, pushups, situps, jumping jacks, etc. You can do them at home and at any time.

Daily activities: Make your daily activities more difficult - take the stairs, park further away, bike/ walk to work/ store, sit on a swiss ball/ at your desk and stand up every time you answer the phone, or lunge/ hop/ jump from place to place in your house. Things like these may seem small and silly, but the increased calorie burn can add up over time. Don't forget a healthy diet!