I have four kids and I honestly didn’t find it much of a financial burden at all. In fact, I would argue that having more had many cost savings.
I was able to reuse things like cribs, baby beds, and clothes by handing them down from oldest to youngest (and many of those original items were given to us at baby showers). Plus, having more kids gave us built-in babysitters, as the oldest ones got old enough to watch the younger ones. And now that the oldest are driving they can even help take the younger ones where they need to go.
With the exception of their private school tuition (which is a totally voluntary expense), I honestly have barely noticed them financially.
I had a neighbor with a very large family. Religious Jews. I was asked him about the expense. His response was something like:
If people added up the cost, no one would have more than one child. What I have is one FAMILY.