This part of a Grant Proposal has two sections: the Budget Narrative and an itemized Budget Summary. The two sections often comprise 2 pages in the Grant Proposal.
The Narrative is written first by reviewing the activities associated with the Project Objectives. In essence, you are reporting to the Grant Maker the anticipated costs for the steps of every activity fulfilling each objective. You are expected to provide "real" cost estimates...not guesses...as well as how you gathered the information. For example, was it by past experience, formal estimates by local contractors or mathematical formulas? Whatever your source, identify how you arrived at the cost of each line item in the Budget Summary. You and you alone will conceptualize the Budget line items and the only "real" research work is to provide data supporting your line items.