And one of the best ways I found to learn was to get hold of a Unix based machine and repeatedly break it/fix it.
the easiest (and cheapest) way to do that is use Linux. And if you are really serious about it, I would recommend going through the pain of building linux from scratch:
Welcome to Linux From Scratch!
It is hard work, tough to understand at times, but the support is great, and the end results leave you with a nice warm feeling in the pit of your tummy. (though it can by no stretch of the imagination be called a usable system, but it is the bare minimum to get you started.
BTW if you haven't already, at some point in the future while you are investigating Unix systems you will be thrown into the vi editor, and at that point you will not have the faintest idea of what to do - remember this ":help<cr>"
Also, here in the UK sys admin ave salary is £35-50,000 or around £400 / day contract rates. depends whether you like rain or not, but we don't bite (much) and our documentaries don't keep repeating what they have just told you 36 times after every advertising break :-)