I got almost all my books from Amazon, ebay or from other students. I also sold them through those same venues. My total law school book cost (considering sales and purchases) was a net of about $500. You should try to make friends with a few 2L students immediately upon starting school, and get books from them. Since the law changes so frequently, it is pointless (in most cases) to keep your old books, so sell them and make some money.
Also, don't bother buying Black's law dictionary. You can access it online at Westlaw, and you will have free Westlaw access all through law school.