It's actually 2000gp for the 1st level spell book, doubled for each higher level (so 4000gp for 2nd level, 8000gp for 3rd, 16,000gp for 4th, 32,000gp for 5th, and a whopping 64,000gp for 6th) but I've always read that as being the total cost per book (i.e. including all spells of the appropriate...