Ok, that explains a lot of things BUT g-ma did relinquish the child to the father. You know dad has been active with things (the court filings) so most likely he did not just up and disappear and nothing sinister has happened.
I understand your angst but honestly, this is not a police issue nor a missing child issue at the moment. It appears as he either intentionally or not, has failed to respond to your attempts of contact and that is it.
As I said, if you have a real concern your daughter is in harms way, you need to get on a plane and head back to Florida and deal with this. If you do not fear for your daughter's safety, you need to simply continue to try to contact the father.
I would continue to check at the school as well.
If you were going to be gone the month of March, why would you need signed agreement. This is his child too. Parents can work together without 72 page legal documents assigning every minute of their child's time to some party. Even you had said for the most part, the relationship has been good.I offered him an agreement that I could file with the court stating that he would exercise additional parenting time from March 1st until March 31st. He did not want to sign this agreement.
I think if an ex really figured I needed to sign some document that would allow me more time with my child, especially if we had a decent relationship, I would be offended.
.if I felt I had to be across the country due to needing to protect my child, I would find the $200 somewhere. Friends, family, and church; I would walk down the street and ask as many people as it took to get $200 if I felt I must get across the country to protect my child.I just felt like I should be doing something. And I'm sorry that I don't have the money to fly back to Florida tomorrow. All the care and concern of the world doesn't manufacture $200

