I think this is A Matter of Profit. Though it is from 2001, so it is probably too late for what you are looking for.
The story is focused on Ahvern, a Nobel of a militaristic Empirethat just conquered a mercantile one, the T'Chin. 39 of the 40 planets in the T'Chin Confederation surrendered immediately, and the last one fell after a short war. Ahvern is suspicious about the easy victory, and after making a bet with his father, does some investigating on the planet. He goes to a bibliogoth, someone who "will teach you how to figure out what facts you need, find them, and organize them in a manner in which you can use them and then put them to use."
The biblogoth is a T'chin, a member of the race for which the confederation was named. The T'chin are described as 8 feet tall ant-like creatures. The biblogoth also charges 1 gold brick per session, and it is mentioned that Ahvern's stipend is only 4 silver bricks a month.