In most cases you must let the child visit out of state unless the order limits the visit to within the state. The divorce or custody judgment may state who pays travel expenses. If there is nothing in the court order about who pays travel costs, the person who asks for the visiting time may end up paying but you may agree to share the costs. You should first try to talk to the other parent to try to work out the problem if you can do this safely. If that fails, you can file papers with the court complaining about the denial of parenting time.
Every county has a special hearing procedure to handle parenting time problems.
Go to the circuit court clerk's office and ask for the parenting time enforcement forms. The court will schedule a hearing within 45 days. Some counties will require you to attend mediation first. You should not need a lawyer to file the papers or to go to the hearing with you. If nothing else works, you should get a lawyer so you can ask the judge for an order holding the custodial parent in contempt of court.