My husband and I are currently in Washington, and our exes are in Missouri and Ohio. The parenting plan for my children is currently in flux, but the one for his kids is:
Every other year, the children spend all of Christmas break (from the day after school gets out til the day before it starts) with their Mother. They spend every other Spring Break with her, and 6 weeks in the summer. She is welcome to visit them anytime she likes, in Washington. They split the cost of transportation, and have since she moved to Ohio from Leavenworth. That didn't change with the increase in cost because the children will be flying now.