You and I seem to be in very similar places right now, and I wanted to come and say hi. I may not be able to offer you any great advise, but I do want to let you know you are not alone.
Right now, you (and myself) are in the midst of divorce. The negotiating part. Not easy for anyone, but the trauma of how many of us here were left, makes this much more painful. The only thing worse was acute Bomb drop. The negotiations all seem to trigger the unfairness of BD as well as many of the issues we had within the marriage. We are still in conflict even though our marriages are over and Once again we feel invalidated, abused, and treated unfairly.
But like BD, we will get through this as well. Just take it day by day and figure out what battles are important in the scheme of things. This will not be forever and you will one day be able to get your life back.
I am trying to cope by recognizing that this part of the "journey" is temporary. We wont be in the trenches permanently but we are now and lets just deal the best we can.
It sounds like both you and your ex want to do what is best for your daughter. That is a really good thing. Its just that you have different perspectives on what is best for her. You feel strongly about the extra curriculars and he does not. Is this the major issue? Or is it something deeper you are fighting against like feeling like all the work regarding daughter fell on you throughout the marriage?
I too, have a child with special needs.(My son has adhd and has recently been diagnosed with high functioning autism) I know how difficult it is to be on high alert every second. And to constantly deal with abnormal behaviors and the relief that comes when you actually do get that good day in the middle of many challenging days with your child. I know what it is like to live with minimal sleep and to have felt that you are doing it all on your own. I know the resentment you must feel for husband because it is not easy and because he bailed. And i know how hard it is to move past that.