Ikariam Finances and Gold Guide by Liarya
Each citizen gives 3 per hour. This means that you will need more citizens if you want to earn more (You get more citizens through more satisfaction. You can get more satisfaction through a tavern or a museum)
Each scientist costs 9 per hour. Some researches like letter chute reduce the cost of scientists.
Each worker costs 3 per hour. (The actual reason is that you loose a citizen who?s paying taxes and so you?ll earn 3 gold less for every worker)
Each military unit costs hourly ? how much depends on the type of the unit. You can find more information in your barracks.
*IMPORTANT*: The upkeep of your units will be divided among all of your cities ? proportionally to the population-size. Relevant to you is only the entire finance result -> it will be shown if you click on the gold icon in the top left of the game