As another already posted, without budget disclosure by the day schools, it’s impossible to explain significant tuition differences even within the same state, let alone address them.
Even taking into consideration differing median income levels between towns (http://quickfacts.census.gov/qfd/states/), it’s hard to fathom how base-line tuition in in the lower grades in my town, for example, is ~$9K/yr while in a town 10 miles away the cost is almost double for the same grade). Where does that “extra” money go?