I'm not a Prayer-Day person myself but many do value it. And the Logos blog has a nice offer available.
Among the bargains, specifically https://www.logos.com/product/3440/an-exposition-on-prayer-in-the-bible
I've noticed quite a number of threads trying to get a handle on Bible treatments of prayer. Well, this one certainly makes a run at it ... all (almost) 3,000 pages (or 19 megabytes). Maybe there'll be future sales at a higher discount, but if you want a good in-depth reference, this would be a good start (on the resource page it looks like they had a hard time on just how many to recommend the book!).
From the Logos resource page (my underlining):
The Bible refers to the word prayer or expresses a prayer in 61 of its 66 books, making close to 1,100 distinct references to and about prayer. Beginning with Genesis, Rosscup identifies each prayer with an introduction and a title that corresponds to its message. He offers clarification of the author, date, theme, and background; provides an expositional outline, with numerous details under each heading; and a brief synopsis of the role that prayer plays in that particular passage or book. Here are pertinent introductions to Bible books, key aspects in settings and customs, flowing outlines and expositions that highlight the relevancy of almost every Scripture verse on prayer, and practical principles to fan a life of prayer.
