I don't know of such a thing, but I was hoping for a reply. I wanted to do a module based on economics a few years ago, and actually spent a while trying to write out a system for how something like that might work. I eventually scrapped it for the story-lite, hack'n'slash PW one I've been tinkering with, but would luv to see something like that.
The module RTS - Harvest of Souls was the closest thing I played to a module that relied on an economy. It, like it's title implies, is a combination or real-time strategy, where you collect resources with your workers and bring them back to your base, and NWN. Very fun.