Sum Formula for Budgets?

I've been keeping a budget using Excel for about 7 years now. I keep a tab for each month that breaks down exactly what I spending and where. I have a tab that shows what I've spent in each category I've created, but what I'd like is to track (on another tab) WHERE I'm spending my money. So, I'd like to be able to add up everything I spend for a month to a specific payee (i.e. monthly total for everything I bought at, say, Amazon). Right now if I want to add this up I have to sort through it myself. Attached is an example month. Help please, I've been trying to figure this out for a while. (as an FYI, I'm using Office 2008 on an iMac).