I would if it was still a school I was happy with.
For me I'd take into consideration the curriculum, size (enrolment) etc of the school, but also how it will affect your kids moving schools, emotionally as well as academically.
You dont want them to think you are putting a new bub nefore them, you know how come kids can think..
It sounds like the school may end up being too stressful finacially anyway if they have such huge price hikes every year, so whether or not you have another child may not even come in to it.
In that case, I would move them to a new school that you're happy with earlier than later, then its not even associated with the new baby if you choose to have one.

Also, Catholic schools in particular (at least Joesphite order ones) can allow you to have unusual payment methods - at my high school one students dad was a stonemason, and he built the front gates and wall of the school in lieu of fess for X period of time.