Question from my Mom

Don't worry, this is a ChildLit related question :)

If you had $500 to spend on children's books for children in the first-fifth grades who also happen to be weak readers (fourth-grade level tops), what would you buy and why? Most of these students are reluctant readers and really need to be drawn into a book.

ETA: This small collection will amplify the school library collection. Budget cuts have been tough the past 10 years or so and the library could use some fresh, fun books.

I'd like to compile a list for her. Tops on my list would be the Babymouse series, by Jennifer L. Holm and Matthew Holm. What would you suggest?