Sign them up as volunteers for these groups. A kid who likes theater can volunteer as a bit part in a play.
A teenager who likes to paint can be paid to help set up paint workshops and supervise painting lessons for younger children and learn how to be an art teacher.
Teenagers can join amateur orchestras and choirs to learn music.
If your child enjoys karate, they can become a junior instruction to the lower belts in return for free lessons for the higher belts.
Music lessons eventually lose their value, and are replaced with simply the need to practice. Have your child or teenager go to nursing homes, assisted living facilities and hospices and PLAY for the audience. They gain practice, social approval and a better appreciation for their own health.
You don't need an instrument to learn music - simply a voice. Join a church choir.
Skip paid sports teams and play with friends. Same exercise, no uniform fees. Or work maintaining the field or picking up trash to earn money for the sports dues.