Army Multiplier
The Army Multiplier is a setting that game creators can configure. It defaults to 10, which means that the first 10 armies each player purchases each turn cost 1 gold each. The next 10 cost 2 gold each, the next 10 cost 3 gold each, etc.
If the Army Multiplier is set to 0, armies always cost 1 gold each.
Games can also enable the purchasing of cities. See cities for more details.
 Reinforcement Cards
Reinforcement cards still produce armies like normal, not gold.
Note that, while it's normally possible to commit in a commerce game without deploying armies, when you play a reinforcement card you must deploy as many armies in the turn as the reinforcement card(s) total. Deploying fewer would waste the armies, so the game prevents you from doing so.
 Local Deployments
When a commerce game is combined with local deployments, the local deployment values should be thought of as a limit of what each player can deploy in each region.
For example, if settings give you 5 base income, and you control Central America which is worth 3 gold per turn, you would be limited to deploying 5 armies anywhere plus 3 armies in Central America. These limits are enforced no matter how much gold you possess.
When the army multiplier is enabled, most of the time you will end up not being able to afford to deploy armies to every single bonus. This actually can allieviate some of the tedium that comes with local deployment games on big maps, as players can choose which bonuses they wish to deploy to and leave undesirable ones un-deployed.