Steve,
I picked a dogeared copy at the Nationals about 5-6 years ago for $10. You might want to keep an eye on Ebay. It seems to me that H.P. books sold a book entitled "How to hotrod your Buick V6" which was the Powersource book with a different cover. I don't think it's still in print but maybe you can find a used copy on Amazon.com.
Neal