I think the issue here is becoming a better diver- or it should be. You can do that by taking an advanced course that combine sbook reading, classroom exchanges, pool and open water experiences, and formal testing and exercises, AND you can become a better diver by diving with others who can offer you insight, information, correction and explanation. They might be instructors, or they might be non-professionals who are really good divers. I think you should combine both forms of learning and growing. If you are serious about it, I don't know why you are trying to save a few dollars on materials. My LDS sells a class like AOW as a unit including all materials, classroom pool and open water sessions. I am sometimes frustrated with students in the AOW class who don't have a compass, or some other item integral to the course and to being an advanced or independent diver. In an era where we spend $500 on a bcd, and more than that on quality and long lasting regulators and computers, do you really need to save $5 by buying a used and likely out of date book? I don't own the shop, I don't profit from instructional material sales. I just think you should have current materials, and an investment in them that will encourage you to use them. There is no cost for materials if you know someone who you can dive with and who will mentor you or lead you to better skills. I do that all the time. As a friend and dive buddy. No certificates are given, just experience and skills improvement. Happy diving!
DivemasterDennis