本の代金を

the cost of the book(s)

→ 本
phrase Rare #41,606
the cost of the book(s) Used as the object of verbs such as 払う or 支払う, meaning to pay for the book(s). The を marks what is being paid.
JA: 本の代金をクレジットカードで払いました。
EN: I paid for the books by credit card.

本の代金を小切手で払ってもいいですか

May I pay for the book by check?

君は本の代金を払ったのか

Did you pay for the book?

そんなにたくさんの本の代金を払うことはできないことを突然思い出した

I suddenly remembered that I couldn't afford to pay for so many books.

本の代金を小切手で支払ってもよいですか

May I pay for the book by check?