Just my humble opinion here: Many feel "guilty" if they don't take an expensive review course, etc. for the boards in order to learn the "real secrets" of the elusive board exam. Again, in my opinion, it isn't necessary. I graduated from a mediocre program and had low prite scores. I studied from one source, and passed the exam the first time with flying colors. Similarly, I also passed the orals the first time following the same strategy.
Firstly, find one book that you like, and memorize it. Second, do a lot of practice questions. Lastly, don't doubt yourself...go in there with confidence. If you aren't confident, pretend that you are.
Keep in mind that attending salaries are coming down in all specialties; resident salaries are not increasing in any significant way. Student debt is at an all time high. Many board certified physicians (any specialty) are finding it hard to manage financially.
Save your money and study on your own. If you don't pass, it might be worth it at that point to invest in a course, but not until that point. $1500 dollars - just imagine how much you might get from putting that into the stock market for the long term. Oil stocks?
Note 1: I studied the Spiegel book, and "Boarding Time" exclusively. Never touched Kauffman.
Note 2: The PRITE is worthless for the boards.