Where I’m at, Legal Aid does assist with at least the child support/custody aspect of things (I was never married, so not sure about divorce). I know because I didn’t qualify for their services in the beginning (and, towards the end when I would have qualified, the attorney I consulted with actually said I didn’t need their services) which is also why I know how the court website in this state is set up. And, here anyway, I did contact some of those agencies mentioned by Ben above and not one of them would TOUCH a custody case, basically because they have such great potential of being very drawn out and arduous.
That might be true even in a state like mine but if it’s a choice between just plain not paying and at least attempting to get the mod, I think people should at least try. Maybe not the best idea, but better to try that than get your license pulled, wind up in jail, and whatever other ways various places deal with noncompliance.
I had a lawyer for the first part of our custody thing and then stopped being able to afford him. I did child support mods, parenting time assistance (had the father put on supervised visits), etc. without him. It’s scary to be a Not Lawyer up against an actual lawyer when you’re in front of a judge but, for me, it was infinitely better than doing nothing at all. That’s all I’m saying. It may not be optimal, but it’s better than doing nothing at all.