Youth football pays nothing unless you've got a nice benefactor at your park that hooks you up with a little extra. Its just parents, former players, community guys, etc. that just want to help out. Considering South Florida has the best youth football in the nation and its not close, the coaching can't be THAT bad at that level.
When you get to the high school level, you get a 5K stipend before taxes on top of your teaching job (or some job you likely have with the school) to be the head coach, a few other coaches might get an assistant stipend 2K and change before taxes. Many others on staff are just volunteers.
I mean, per dollar, its the best coaching in America. Most programs, even the top ones, are nickel and diming the entire operation from staff to facilities, etc.