The book "Costs Book" does not appear to be a widely recognized or well-documented title in the search results provided. However, there is a publication titled "The Costs Book" or "Legal Costs Victoria" edited by John A. Ahern, which was published from 1975 to 1987 and then continued under the same editorship from 1987 to 1994. This publication seems to focus on legal costs and might be a collection of articles, case studies, or guidelines related to legal expenses in Victoria, Australia.

Given the lack of specific information about a book titled "Costs Book" by Jill Grace, John A. Ahern, or Robert Allen, it is not possible to provide a comprehensive overview of such a book. The most relevant information available pertains to the publication "The Costs Book" or "Legal Costs Victoria," which is a series of legal cost guides edited by John A. Ahern.

If you are referring to a different book with this title, please provide more context or details, and I can try to assist further.