A project proposal has several components such as project goals, objectives, results, strategies and activities. With so many sections, how and from where you can start the process of developing a project budget.
An ideal way of starting to develop a project budget is to look at your project activities. Although the project development process requires you to go back and forth from goals, objectives to strategies and activities and back again, but once your activities are ready, then you have achieve a great level of clarity.
No matter how complicated the budget format of a proposal application is, the first step towards developing a project budget is to first note down all your activities and then attaching costs to them. This is the most logical and easiest way to develop a budget for a proposal.
Source: https://www2.fundsforngos.org/cat/develop-budget-project-proposal/