Reply to the following There are multiple cost methods used in my organization. I have seen the Bottom$-$Up method used in multiple occasions in order to obtain specific equipment and training. The DoD teaches the use of four types of cost estimation methods in the Defense Acquisition University $($DAU$).$ The methods are Parametric, Bottom$-$Up$,$ Analogous, and Actual Costs $($DAU$,$ N$.$D$.).$ The PMBOK Guide discusses three of these, except the Actual Costs. Instead the PMBOK Guide discusses Three$-$Point Estimating.

In my opinion, I think the Parametric and Bottom$-$Up methods would be pretty accurate. Parametric method you are obtaining historical data and in the Bottom$-$Up you are getting the information from the source. The Analogous Method looks at previous similar projects to estimate the costs for your project. The problem with that is that material prices could have changed, certain materials may not be available anymore, or for instance since COVID, prices have skyrocketed for everything. Previous projects would no longer reflect what the prices are now.

According to the DAU, the Actual Cost method utilizes, "current contract cost trends are used to estimate final system cost. The cost data is internal to the current system being constructed, which is not the same as $$actual$$ historical data" $($DAU$,$ N$.$D$.).$