If you can ever make it to the point of being a collegiate coach...totally seeing even at the bottom they probably make 55-70k/year and I've heard some of the bigger schools pay 6 digits halfway towards 7. As an assistant...well that probably doesn't pay that great but ok considering the job.
One of the biggest issues is Full Time hours. Quite often a full time schedule for a coach is still not 35-40 hours but they might get salaried at that point (and end up working a lot more than 40 hours but we all do anyways).
As a recreational coach, it's doubtful. Perhaps someone at Steve Greeley's gyms might get on by but not any standard rec gym. @ best at one rec gym, I think pay topped out around $15/hr for management. Both managers eventually aspired to moving on to other professionals because it did not pay enough long term.
At some big gyms, that are highly successful, you might get decent pay, benefits, etc.
Now keep in perspective that out there are familes that get on by making $10/hr with both partners working FT though some might have jobs on the side or other PT jobs.
In the bay area, our FT coaches made 40-48k/year. Sounds great but isn't considering North Bay cost of living. I made decent $ as a PT coach @30-35hrs a week but my 1bdr apartment@ 1100/month was killing me. It was like 50% of my salary. I really should have tried just finding a room to rent somewhere. Now, maybe if I had a partner at the time...cost of living would be a lot better but it's not so easy finding a live-in one of those.
Pretty much in club gyms, the only ones making really good money are the owners. I knew of a former Olympian, one of the greatest ever who made about $30/hr but didn't have FT hours in the Bay area. His wife was a coach as well, but just a lower level coach.