How much time do you want to spend on the project? I bet you could build something pretty nice given a few weeks of work. Will it be worth it? Think carefully before answering. I have a hunch you've drawn yourself up a nice technical challenge that probably isn't justified by the required functionality.

Of course, it does sound like a lot of fun! I think I'd model a solution based on filter configuration systems ala Outlook. Basically a GUI that allows you to configure a series of rules that are then evaluated for each record. You'd have to pre-define a series of available functions and fields, but otherwise it could be very flexible.

-sam