Sometimes, the Internet Archive (archive.org) has a digital scan available for borrowing (usually for 1 hour or 14 days) just like a physical library. This is a legal, free option if you don't mind waiting for a "copy" to become available.
The book is published by Zondervan (a HarperCollins company). You can purchase All the Prayers of the Bible on Amazon, Christianbook (CBD), or Google Play Books. Prices usually range from $9.99 to $14.99. Once purchased, you can read it in any Kindle or EPUB reader app.
For decades, the late Dr. Herbert Lockyer (1886–1984) was the gold standard for topical Bible study. While he is famous for his All the Women of the Bible and All the Parables of the Bible , perhaps his most practical work is All the Prayers of the Bible .