I've seen this topic way too many times, and I've bought and/or read most of the LSAT books out there. Here's a list of what I believe is the most cost-effective study package for the LSAT.
First of all, most Kaplan & PR books can be found in your city's libraries, so check first before buying them. The following is a list of must have books.
Powerscore LG Bible
Powerscore Games Setup
Powerscore LR Bible (not available yet)
10 Actual, 10 More, and Next 10
PrepTests 39 to 42
I did not include Master the LSAT in my list b/c I found the book to be too basic. I didn't find anything that was really helpful except the LR diagramming technique, which I ONLY ever use for parallel reasoning questions. Paying $30 for a whole book for just a few pages feels like a waste to me. I found the Kaplan and PR books to be more helpful than most people give them credit for, so definitely skim through them if you get the chance. The LSAC Tripleprep and Superprep kinda sux, the explanations are really weak and do not explain very well. You're better off by just doing the questions and think really hard on why you got the answers wrong or just check with this board. By far, all the Powerscore books are better written than the competition and more helpful; you MUST buy them all.
My biggest regrets are buying the Master the LSAT book, a PR book, and Superprep from LSAC; I wasted about $100 =(. For an independent student, that is a lot of money.