Can he just provide his own insurance to cover the child?

He should be able to do that. If your son can simply add his own son to his existing medical insurance coverage, and do so for less than $400 a month, the court should allow him to do that. But your son cannot act on his own, without approval of the court. if I were him, and I wanted to have the court approve covering my son to my existing insurance so that I don't have to pay $400 a month for a different insurance policy, I would file a motion with the court asking the court to issue an order granting my request, and I wouldn't disobey the court's order to pay $400 a month until I had a new order.