I’m confused.
Do you pay one application fee which allows you to submit applications to as many prep schools that you want? Or, do you pay an application fee for every school you apply to? It seems like fees would start adding up really quickly if you had to pay an application fee every time.
You pay for every application. Yes it gets expensive! (There are few waivers available if you qualify).
Oh… I was planning to apply to quite a few boarding schools. I guess I really have to get strategic with the amount of schools I apply to.
Another factor to add in is the cost of visiting/interviewing. While some schools do not require an on campus interview, you really should visit your top choices. Things look a lot different in person than on the internet! NE is a huge change from South Carolina.
You also can save $ by only visiting the schools that offer you a spot 
I just spotted a typo on my part — there are FEE waivers available (not “few”).
Also, remember that it takes a fair amount of time, energy and work to apply to each school, so that’s limiting, even if the money were a non-issue.