I have two friends who minister in homeless shelters and women’s crisis centers. They do Zumba, which appeals very very well as it’s an inclusive, fun format. (My work with teens and young adults is through Zumba but it’s a little different because I fold special needs students right into my regular class as opposed to going to a separate location. At any rate, they flourish with the music and the dance)
Another thing to consider, if it’s within your scope, might be some kind of yoga.
A place where I used to work has a separate non-profit organization for kid and teen health where they train at-risk youth and youth who can’t afford a gym membership or personal training. They do the standard bootcamp sort of classes, indoors and out.
In my opinion, the most important thing is the consistency of your commitment.