I have been writing a campaign over the last month. We have six PC's and they each have partnered up with one other person to run a kingdom. There is the 3 PC kingdoms, as well as all a few other NPC kingdoms that I am running. I already have the base stuff each kingdom starts (depending upon location) but I need help with the basic things. How much income would a mine bring in or a farm or any type of resource that holds kingdoms together. What does it cost for upkeep on this. I am trying to keep the prices fair (based on location) and I am not quite sure where to start with this.
Are there any published rulesets adaptable to D&D 3.5 that support this style that I could use?