1) Marc Lawrence's Playbook Football Preview Guide - usually out the last week of June. Great team write-ups and articles, along with tons of trends. A must-read.
2) Lindy's Pro Football Annual - Bought my copy today at the newsstand! Lots of good player info and a coaching roster for every team.
3) Athlon Sports Pro Football Annual - Bought my copy of this today too! Also has good player info, along with great info on all the different coordinator changes.
4) Week One NFL Winners - 2019 version on sale at Amazon now. Over 100 pages of analysis for this year's 16 Week One games. Tons of coaching history info. Must-read.
5) How to Beat the Pro Football Pointspread by Bobby Smith. A really good book with some great handicapping advice.
There are other good ones, but they are out of print and difficult to find. The ones listed above are all available and on sale now.
If you bought them all, the cost would be between $25 and $50, depending on whether you got the Kindle or paperback versions.
A splendid investment for anyone betting $50 or more per game. If you can only get one, I would go with Marc Lawrence.