It costs $100 to file a petition to modify a Utah divorce decree or Utah child custody/paternity order.
There are also costs associated with service. Once you file your petition to modify, you have to have someone serve your ex with those documents.
The Utah Rules of Civil Procedure specify you can’t do that personally (too much room for monkey business), so you should have a professional process server do it. That might be a constable with the sheriff’s office, or a company that serves these sort of documents regularly. Either way, the cost will likely range from $15 to $50.
All told, the cost to file and serve a petition to modify in Utah is around $130.