If you were given a money judgment, you have 7 years. You can also file a petition to extend the 7 year period. If there was no money judgment and there was just an order to pay, you can file a petition for rule at any time. Discuss with a lawyer who can review divorce judgment and give you a more specific answer.
For this small price litigation will cost far in excess. I'd try to reach an agreement that she pay hers and maybe you pay $100 toward the balance, if the total is $400. If it's not in your agreement you should review again allocation of liabilities If your marriage is long term the ultimate result if you shared assets equally is to allocate this cost in some way.
you should consult with a lawyer in the state in which you were divorced. burt gave you an illinois law answer. mr. the gave you what is probably a Massachusetts answer. if you asked from ohio i assume that is where you were divorced. your answer then lies within ohio law.