A.L.
I am about to take it as well. The ETS website where you register for the GRE has some free practice questions on it. They also have free prep software and materials.
I also have a preparation book that was relatively inexpensive that has a number of free tests, your library may have more as well.
I have found a bunch of apps as well which are great for learning vocab (not so great for math).
Inquire at your target school whether you should take a subject test as well. Make sure you talk to someone in the department you are applying to, preferably the professor you would most want to work with.
My school's official application information says it is not "required" but I talked to faculty who regularly sit on the graduate admissions committee and they told me that usually they don't even look at people who haven't taken the subject test... that was quite a surprise for me as I had not intended on taking it.
I have been leisurely preparing for a few weeks, starting in earnest this weekend 4 weeks out. I have looked through everything and would say that none of the materials tested are terribly "hard". A lot is memorization and recalling stuff from high school, particularly in the math part. The test starts off with two 30 min essays, those you just need to get into a habit of writing. The entire test is more of an exercise in time management and staying focused, rather than real knowledge.
Good luck.