Each structure requires one supply unit and megacredits to build. The cost of a mineral mine is 4 megacredits. The cost of a factory is 3 megacredits and the cost of a defense outpost is 10 megacredits.
Mineral mines extract minerals from the planet when at least one the four primary industrial minerals are present in the planet core. Use the mining survey screen to see the minerals present. A factory produces one supply unit each turn. Supply units can be used for building more mines, factories or defense bases. Supply units can be sold for 1 megacredit each or transported to other planets in the cargo holds of starships. Defense bases protect a planet from attacking enemy ships. Consider it the last line of defense.