well personally i would say, save yourself the 100 dollars and just read ...
so with that said i would say the best source for learning linux, and the best
source for everything else, is www.google.ca
i am not trying to be sarcastic
but its the truth ... just search for stuff .... and to make it more "reliable and accurate"
and i dont' know what you want to learn, or where you want to start but i will
link a few things to get you started ...
(from beginning to end - READ THIS - highly recommended)
(filesystem breakdown and explanation)
(a more detailed look at the filesystem)
(TLDP - the linux documentation project - contains all the HOWTOS)
(shortcuts and commands)
(a couple more shortcuts)
(20 Linux tips)