I’m not going to judge anything about the OP’s relationship with his daughter or his ex. I know enough about divorces and custody to know that there’s always two sides to every single story.
What I do know, which is what I’ve been saying from my first comment, is that in the world of divorces/custody, when there are significant changes in a parent’s finances, the way to handle it is by petitioning for a modification to the order. It’s done all the time. In many states, it’s pretty straight forward to do without an attorney if the circumstances are straightforward and well-documented. If the OP’s finances have changed significantly, he needs to file for a modification.
My main point is that, even if the order is modified to take into account the steep rise in college costs over the last 15 years and his businesses losses, it doesn’t erase the fact that he’s known for 15 years that there will come a day when his daughter will come to him expecting him to pay for college. And if, during the last few years while his daughter was doing so well in high school, he hadn’t given any thought to how much college actually costs, or how financial aid works, then he’s not any different from the parents I mentioned.
FWIW, one of my closest friends has a child he’s only seen a handful of times in the last 8 years because of his ex and I know full well what a horrible thing that is to do to a child but, in the U.S., child support and other financial obligations are never tied to visitation/access. Denying access never relieves the financial obligation of the non-custodial parent. I’m pretty sure the OP is aware of that. But given his ex and the history he paints, I’m surprised he thought his ex would cooperate in lowering the costs he’s ordered to pay.