Usually it isn't expensive for the mother. Not so for the father. Besides that I've never heard of a recent case where a father got his support *lowered* for any reason. Not for being laid off, not for being injured on the job or off, not for getting sick, not for being a victim of a flood, fire or hurricane...not for any reason.
Reason being the judges and CSA's work together. Keeping support orders high enables the state to get more federal kickbacks. The state can spend that money on anything they want to...they don't have to account for the money to anyone. Judges can't by law get kickbacks but they do benefit by receiving higher retirement benefits. You yourself admitted you hadn't practiced family law in a long time. Things have changed.
I will say though that every judge is different, as are child support lawyers. I suppose sometimes there might be a judge with a crazy agenda or some crazy feminist child support lawyer out to nail all men to the wall. What I see in my area though is that the child support enforcement lawyers are actually pretty reasonable and in many cases when they do there regular reviews of cases they've even asked for downward modification if that was really what was warranted. And with our local office the policy is not to go after large past support judgments in initial support orders. They feel like that if the noncustodial parent had have really wanted the support they'd have gone after the custodial parent in the beginning and not let months or years pass. Besides, if the ongoing support or past support judgments are too high it just makes their jobs harder, and some of them believe it or not are pretty fair and decent people.
Where I see things being hardest on noncustodial parents is in criminal court on criminal nonsupport charges. In civil court where they deal with these cases all the time judges here at least give people a lot of breaks. They see the same people all the time and they know how tough things are and they are just trying to collect as much support as possible without putting kids’ parents in jail all the time. In criminal court judges are trying to set examples and the last thing they want is to have to deal with the same faces over and over again. They see these people as any other criminal and they hammer them hard. I saw a judge a while back tell a lady whose support was $120 a week that if all she made was $120.67 she was by God to pay a $120 and live on the sixty seven cents. He didn't care if her income didn't warrant the support amount she was ordered to pay or if she couldn't afford a lawyer to get her support lowered, his job was to see that she followed the law and he was by gosh going to do just that. She'd been paying regularly, just not enough, and he put her in jail for ninety days. Most of the judges in civil court around here would have given her a break because at least she was paying something, unlike a lot of people.
I “admit” I haven't practiced family law in a long time? You make it sound like I'm trying to pull the wool over people's eyes or something. I'm just passing on my personal experience to add to the conversation here. Your mileage may vary. Things are different in different places.