The upkeep costs of armies are at the high level they are to limit the amount of armies you can have and to prevent the game from becoming too easy. However, if you really want to, you can change the upkeep costs of units. Unfortunately, there is no way to do this in notepad without individually changing each unit's upkeep. You could however change the file to an Excel like format and highlight the whole upkeep collumn and lower it by 10 or 15 percent.