Santa Monica Community College has a comprehensive online tax course that covers a lot of the tax material and the class doesn't cost that much. That said, they recently implemented a two tier per unit cost. But even then, it isn't that expensive considering what you'll get.

Or you could buy the South-Western Federal Taxation (Comprehensive) textbook by author Raabe. It'll take you three months to study all the material. Don't buy the tax textbook by CCH. It's not as user friendly as the SWFT textbook.