ENDED: Several cheap books for 7 and 9 year old girls

[TheCaber]

Wild guessing, not knowing geolocation or reading levels/preferences of the 7/9 y.o. girls:

AbeBooks: https://www.abebooks.com/
Scholastic Books: https://www.scholastic.com/home/

GoodWill store near you?
Dollar Store? Dollarama?

Authors to consider:
C. S. Lewis (Chronicles of Narnia series (7 vol), Perelandra series (3 vol))
J.R.R. Tolkien (The Hobbit, The Lord of the Rings series (3 vol))
Madeleine L'Engle (A Wrinkle in Time series)
Roald Dahl
Beverly Cleary
R.L.Stine (Goosebumps)
Dav Pilkey
Carl Hiaasen
Cornelia Funke

Is this at all helpful?