The cheapest way to do it I would have thought is to buy the books, read them until you understand them then complete all the exercises within the book.
After that, I used the ppl confuser which is as accurate to the test as can be. Once your getting high marks using the confuser, get the actual exam done. I found that I had over studied (which isnt necessarily a bad thing).
If you are struggling with something in the exercise book and think that the cd rom might be the answer, you usually find that most instructors will take the time out to explain things from the book to you.