$ Budgets, Custom Fields, Reporting

I am majorly struggling. I was hoping to estimate budgets for projects (NOT hourly related), and export a report that rolls it up into my total monthly expenses within a folder. Without creating 12(+) custom fields or doing a ton of math or excel manipulating on my own. It would be great if I could keep them in a separate category (author vs design expense) but get the monthly total of each, but that doesn't seem possible with custom fields & report features. Am I missing something?