Thank you Rebekah for your inquiry. Your international work is very impressive.
The Community Tool Box does provide some materials on developing budgets in general see:
http://ctb.ku.edu/en/table-of-contents/finances/managing-finances/annual...
What are the elements of an annual budget?
Why should you prepare an annual budget?
Some practical considerations
Planning and gathering information to create a budget
Putting it all together: Creating and working with a budget document
The specifics on your budget will depend on the form of needs assessment that you decide to perform. Would these be on-site teams using checklists? Or interviews with local key informants and institutions? Survey instruments? All of these will have different cost structures. So there is no easy set of tips for developing a needs assessment budget. We would be happy to attempt to answer follow up questions. Best wishes on your important work.