What's your opinion? Divorced with kids and living in different states

To the ladies who are divorced and with children... i relocated in 2015. In 2016 my ex husband took me to court for child support and modification for child allocation. I was granted permission to remove my children from the state and it's a joint custody, I also get child support. He can have the kids during summer vacation, we would share the flying expenses meaning he pays one way, I pay the other. 
He's closest with my daughter. I told him that if he wants her this summer he should pay to fly her out to him and that when it's time to come back home that I would pay to fly her back to me. Does this seem like a good agreement? I don't trust him and we're not "cool" with each other. I don't wanna pay for her to go to him, then have to pay for her to come back because I know he will say he doesn't have money to send her. Going forward I believe this is how it should be done. If I want her here, I pay. If he wants her there, he pays. What are your thoughts?