According to the Washington Post in 2014, NYC spent $20000 per student in public school. The national average was $10600, many school districts spent less than $7k. In public schools there are teachers for subjects like art,music, and gym. Many also have sports teams. Yeshivas have none of these subjects, and they pay their teachers lessthan the pu lic schools.
So yes, I believe it costs the yeshivas less to educate one student, and anyone paying full tuition is covering for those who can’t.