Interestingly enough, where my sister lives in South Carolina, you are hard pressed to find a family with less than four kids. Its very affordable and a good place to raise a family, whether Catholic or Protestant.
St. Anthony's Chapel in W. Orange has several large families in the congregation. One of the mothers is expecting her 10th child in the next couple of weeks.
Regarding the cost of living, it is true that these families are not living luxurious lives. My parents, as a professor and high school teacher, managed to raise six kids in Short Hills. As the youngest, I received my share of hand-me-down clothes. It can be done. One just needs to know clearly what their priorities are.