The personal trainer at my gym makes a good living but he busts his ass. 3-4 hours of group classes starting at 6am, 5-6 hours of private clients, then another 3-4 hours of group classes starting at 5pm. He's there pretty much all day Mon-Friday and half day on Saturday.
He's a well-known competitive powerlifter so guys come from all over the area to work with him, and he does some damn good group classes - I sometimes take his Bodyweight Training Boot Camp group class on my rest days. Most of his clients range from guys looking to start weightlifting all the way to guys that do competitions and want more of a coach.
Definitely has a decent niche. Helps that he's legit a great guy as well.