I got a 153 on my first test (taken under testing time/conditions) after reading two chapters of the Logic Reasoning Bible and nothing else. Within four weeks of having done nothing more than reading more of that book, I took a few more and all were in the 159-161 range. Then I got the Logic Games Bible and my last three practice scores were 164-168-168. This was with no class and only buying two books (the LG Bible and a book of official LSAT prep tests... I had the LR Bible on PDF). So you could very easily score significantly better without spending the cash on a course. I would, without question, get the two Powerscore Bibles.
Of course, then I take the December LSAT, get the same amount of questions right (with the same number of total questions) as I did on both of my 168s, but the curve from hell rears its ugly head and it's only good for a 163. But if I would've had just another two weeks to study on my own (I didn't finish the last three chapters of the LR Bible) I probably would've done better. I just decided too late to take it and wanted to make sure I'd get in this admission cycle.