Being a big fan of productivity, I would recommend toodledo.com. While it's primarily a task management tool, it can be used for Project Management. Probably not for managing a complex software development, but perfect for a wedding.
From the budget point of view, you can use the Notebook feature to track associated costs. The Notebook also includes a timestamp button that you can use to track updates made to the Notebook.
So let's say you had a folders called Decor, Catering, Hall, and Photography. In each folder (from the Tasks perspective), you would track the tasks, deadlines, and priorities for each folder. But in the Notebook section, you can track the budgets for these categories as well as email threads, contracts, and so on.
The pro version of Toodledo includes a file manager. Sadly, this cannot be linked to folders, but you could you put a note in your Notebook like, "Photo_Budget.xslx file uploaded".
Let's face it: It'll be pretty hard to find a tool that matches your needs exactly, so use one that will at least help you consolidate the best of each software (Excel for Budgets, Word documents for email threads, contracts). All of these should be documented in a single "point of contact", i.e. what I recommend: ToodleDo.
Hope that helps.