Way way wayyyyy too expensive for what they are. At least as far as the Final Fantasy guides are concerned if they are indeed just hardbacks in a 3 part case like the "mock up". These are just game guides. Unless this is limited to something super small I don't see them pulling more than $20~/book in the set. (So around $60)
Now if they were like the Hyrule Histora I'd be willing to pay more/book as that would actually have "new" things in it.