Both custodial and non-custodial parents moving out of state, who pays travel?

I moved with my children to Nashville from Denver in February. Now my ex-husband is moving to Albuquerque from Denver. Does he need my permission to move? There are no direct plane flights from Nashville to Albuquerque and unaccompanied minors cannot fly on non-direct flights. My son is 7, he cannot change planes. My daughter is 11, but the airlines go by the youngest child's age. Because my ex is moving to an area without a major airline hub, should he be responsible for purchasing a ticket to meet the kids in the connecting city and taking them back to Albuquerque? When we drew up the new parenting plan he was living in Denver and this was not an issue. I am financially responsible for the first 3 trips per year, he is responsible for all others. His move increases the travel fees by hundreds of dollars and he is saying that I will need to purchase my own ticket and fly with the kids to the connecting city.