There is a parkour/ninja gym in my area with several locations which does quite nicely for itself. They got into the birthday party business, and run a bunch of kid's classes in addition to providing training for adults. About 3/4 of the employees have been on the show, at least 2 have been to Vegas, according to their online bios, but no one I remember ever having heard of. So in the right market, and with some smart management, running a gym can work out pretty well, even if you're not a superstar ninja gym owner like Drew.