Ex owes 25,000 ,not paying and now in SC. Attorney said it could cost 20k with no guarantees of collection. What can I do?

This is not a debt collection question, its a child support/family question. I am changing the category. You should be directing these questions to your attorney. I am not sure why it would cost $20,000 - I suspect the situation is more complicated than is being presented here.

You can commence an action where your ex is located, and see if you can garnish wages and/or collect against assets where he is. Under Full Faith and Credit, the Courts of each state recognize the power and jurisdiction of the other, thus you may even be able to obtain a judgment in New Jersey which is enforceable in South Carolina. You should consult with a South Carolina attorney who may be able to better guide you.

You need to take the New Jersey order to South Carolina or better yet have an attorney to it for you. It will not cost $20,000 to send a new jersey order to South Carolina for South Carolina to start enforcing that order.

If you have an attorney then you should follow his or her advice, however, I don't understand why it would cost $20,000. To fully answer its necessary to know where the original court ordered was issued. If New Jersey and you and the child still live in Jersey, you can work through NJ courts. You should also ask the court to have the child support including the past due amount paid through probation. NJ would garnish the money and direct deposit to you. Are you sure the lawyer didn't say 2,500?