Studying for the OAT!

I am having a very difficult time trying to find good study material for the OAT. Some people say to study from the MCAT books. Is that what I should do? I also wanted to know if the Kaplan classes for OAT are worth it? Do they give you all the materials you need to study for it. I wanted to do well on the test but at the same time, I don't want to shell out $1000.00 for a Kaplan class unless I really have too .Any suggestions on any kind of books that help will be greatly appreciated. Thanks so much!