The first thing to remember is that this is your child.
With that said, the non-custodial parent should provide regular child support for through payroll deductions, etc. as provided by your state's guidelines and also help with 50% of medical, extra curricular activities, and other misc. needs. I know it is difficult, but as I said initially, it is your child.
One thing that I did,I started documenting some of the items that I did that was extra, but considered basic needs for my child ( I paid 100%). I then negotiated with my ex wife to eliminate some of my responsibilities for the 50% medical, etc. By having the documentation that I provided some of the basic essentials, that she did not provide or would not provide, I was able to to show cause for not paying some of the additional 50% expenses.
Hope this helps.