+ Remove them from their shelves, and send a letter saying they do not have the books available. This is the cheaper/easier option, and several schools have already opted to do so.
+ Make a count of all the books, provide location information about the storage of the book, including its exact geographic location on their campus, and trawl their records to determine precisely how much they spent on each of the books in an itemised manner [0], and send a report detailing all of this.
[0] Schools receive books generally in either donations, or in groupings that are not itemised, making determining the cost of an individual copy of a book extremely difficult. That's before you get to poor financial record keeping that is also rife in school libraries.
Do you have a source reporting that schools are actually removing books in response to this particular inquiry? It seems that they shouldn't be. (I am aware of other instances of books being explicitly removed from school libraries or curricula by the school boards.)
What makes me skeptical is that I'm not sure in what situation physically removing a bunch of books from the shelves would be cheaper/easier than retrieving records about them.
Schools don't buy individual books. They buy packages. Those packages are not itemised, and the receipts don't list which individual books you received, just the number of titles in what genres. The people sending the packages don't have that information either.
You make a purchase, and get a guarantee of N titles, in X genres. The warehouse pulls down N titles, in X genres, with varying numbers of each individual title, and then sends that out. The individual titles come from the publisher under wholesale costs, so individual purchases aren't tracked.
The exact costs are further complicated by other discounts that may be applied. Seasonal discounts for different genres, some places will give you discounts if you return covers of damaged books (as proof of destruction), etc.
The records requested may literally not exist, and require the school to compare when entries appeared in their tracking system, as compared to when a purchase was made and received, reverse-engineering those costs.
I found an example of what you were referring to though (thanks to @shankr linking to a relevant Twitter thread). [1]
[1]: https://www.granburyisd.org/site/default.aspx?PageType=3&Dom...
Some State Rep has inquired about these, so is true that it's plausible that some of the books in the list may be targeted in the future, but that hasn't happened yet.
It's quite literally a list of targeted books.
Link to the inquiry: https://static.texastribune.org/media/files/965725d7f01b8a25...
EDIT: I learned of one instance of books already being "temporarily" removed by a school board [1] triggered by this inquiry.
[1]: https://www.granburyisd.org/site/default.aspx?PageType=3&Dom...