I'm building a campaign that includes a Plutocracy style government. The several wealthiest people in each city govern that city, and the wealthiest of those join to govern the entire empire.

I anticipate certain party members will be interested in acquiring enough wealth to join the government. However, I'm at a loss as to how wealthy those people would be. I can calculate basic averages from running multiple large businesses over the course of years, but that doesn't account for inheritance, investments, or other large scale wealth generating activities not covered in the rules. 

Are there any official or unofficial sources that suggest such wealth numbers in the Forgotten Realms?