I would search for summer reading lists from schools that still have lists. Here is a link to a list from a private school in our area -

http://inside.episcopalacademy.org/...pper/readinglistspages/usrecreadhome.htm

There is some classic stuff, some newer stuff on the list.

I don't understand the school district needing to provide the books. Choose some for which the school (or the local library) has plenty of copies or choose ones for which there is a free digital download. I just purchased my rising junior's required books, but I think we could have borrowed them from the library (hard copy or digital). In any case, the school always works with families if there is a financial problem. However, it is an area where even the "poor kids" (in a relative sense) are from families with an income well above the US average.

And here is a link to our county library "lists of summer reading lists" - it includes private, parochial and public schools.

http://www.delcolibraries.org/summerreading13.htm