Here is a view of the Summary page, which dynamically updates based on the drop-down in the upper, left-hand corner.
Can't really go into detail without knowing more about your data model--the tables and relationships that store the data that need to be accessed to produce your report.
One option is to set up a summary report where you simply perform a find for the records you need in your report and then sort them to group them by budget category. Sub summary layout parts can then be used to set up sub headers and to also display sub totals for groups of records in this report.
Here's an old but still valid tutorial on summary reports that illustrate what I am discussing: Creating Filemaker Pro summary reports--Tutorial
If you have any questions/comments about that tutorial, please add them to your thread, not the tutorial. Comments posted to it will not automatically push that older thread into Recent Items so I am not likely to notice that this was done.