Sounds like an urban legend to me
No legend here. The woman's friend Kathleen (whom I know personally) actually came to Father Dean because they wanted to know if they needed to restore the book with the $20,000 in it. He has shared this on any number of occasions when speaking of the treasure we have in the Word of God.
At any rate, with the Bible we have much more than $100 on every page; we have the revelation of God Himself. And that's no legend. :-)