I used Dr. Collins extensively when I studied for the PCAT and took it back in September. I bought the Kaplan book prior to that and studied off of it, but sadly, what I studied in Kaplan didn't show up much at all when I took the test. I much preferred Collins over Kaplan.
You can find people looking to sell Collins in the Free Classifieds sub-forum here. They almost always sell it for around 1/3 of the full price, which is like $100. Only buy from the Collins website if you cannot find a seller because $325 for the study guide is an absolute rip-off. But then again, I ended up buying it for that price tag because I wanted to score high, and I did.