If you were hareidi and become “modern orthodox” you will probably be better off economically. If you were anything not shomer mitsvos (conservadox, conservative, reform, assimilated) becoming “modern orthodox” will almost certainly create severe economic problems. Once you give up working on Shabbos and yuntuf, and keeping kosher both at home and at work, you pay a serious economic penalty. The line where the penalty kicks in is the one the separate “Modern orthodox” from non-frum. Having to adjust your work schedule to the Torah calendar seriously limits career options. Keeping kosher even if only the “ingredient kosher” that lets you have a tuna salad while your colleagues are having steak, means you suffer serious restrictions.
Having children isn’t really a function of “Modern orthodox” vs “Hareidi” – from the point of view of most Jews (who are not Shomer Mitsvos), the “Modern orthodox” also have “too many” children. Education for “Modern orthodox” is probably more expensive since they want both a Jewish and secular education (and good universities are vastly more expensive than a yeshiva).
I believe many hareidim don’t realize how much mesiras nefesh the Modern Orthodox have, and it is probably all the more painful since they are so close to being able to benefit from the outside world, but are just inside the line. They are inches away from being able to grab the golden ring of the secular world, and are refusing to grab it.