Simple. A locally researched unit price book provides greater visibility into actual construction costs likely to be encounter.
Sure, you might consider using a national average reference cost book for a Job Order Contract (if allowed) and attempt to make it relevant to your location by using a localization factor. However, logic, experience, and research would quickly cause you to rethink that approach.
“A previous study of CCIs conducted …. uncovered a major issue in the use of
these indexes at the project level. That study found that it was unreasonable to believe that a single index number can be used to adjust all types of projects due to the nearly unpredictable impact that dynamic changes in the construction material commodities market have on different types of projects; for example, concrete bridge projects versus asphalt paving projects” (Rueda and Gransberg 2015) – (quotation from 2016, Jorge Andres Rueda Benavides, Indefinite Delivery/Indefinite Quantity project selection framework using stochastic techniques)….
“…the analysis determined that the general principles and assumptions associated with the development, maintenance, and use of these indexes make traditional CCIs unsuitable to be used at the project level in IDIQ contracts.