I advocate making this as clean as possible, by separating the issue of child support payments from the cost of travel and visits.
Perhaps, "Let's agree that if we ignore travel, the child support payment is X."
Now you can focus on just negotiating your H's travel costs... which is going to be challenging in its own right. But hopefully that untangles the emotions of b-day gifts and BTS supplies from the fundamental issue and helps you decide what you want. I think that problem on its own is incredibly complicated.
