Does he go for science fiction? I liked Starswarm by Jerry Pournelle as an adult, but think it's intended as YA. The main character is about your kid's age, an orphan in a extrasolar colony. Thanks to some things his parents did for him before they were killed, he knows some things the adults in charge of the colony don't. Including that the native life on the planet is more intelligent than assumed, and advanced enough to defend itself from human encroachment.

See if your local library occasionally runs a booksale. I get most of my books that way. Their prices are competitive with thrift stores, usually about $1 paperback and $2 hardcover. But because it's run by friends of the library, tends to be higher quality and better organized. At those prices, I can afford to be disappointed, and sometimes get pleasantly surprised.

"Dying cost nothing and could be done at home. Otherwise old man [I forget this character's name] might have lived forever."

From The Rosewood Casket by Sharon McCrumb.