Sounds like the real issue wasn't your kids' activities it was the new house, the sugardaddy feelings, etc. I do the same thing with my H. He wanted to take this over night trip and I got all upset about the money. Really about my upset that he is paying for his own apt. lawyers, everything else. Not the trip. So it's hard, but the task is to try to separate it out. Don't get baited into arguing about something else like your kids' activities.
What I do is go off my myself, talk to a friend, talk on here, journal, whatever to sort out my own anger and pain. Then if and when there is a chance to really talk to my H about this and he is in a place to really hear it, then it can be about the real subject. If H and/or I can't talk about that, I deal with my feelings on my own and try not to get into it with H. There's no point. Otherwise, it will just be a big fight.
On the other hand, if she (or you) can't stick to the topic of your kids' activities without all the other stuff clouding the discussion - which of course it will this is totally understandable - just walk away until this topic can be resolved without the other emotions. I would maybe send her an email or something brief about the activity you support because it saves a few pennies. That is really good and to the point. Make sure she sticks to the point or drop the conversation.
