I know unit cost goes up because of 1) New Era and 2) Upgrades

But in my current game (Era II) I just saw my units go from 164 industry to 204 industry without either of those things changing.  What else is there, or is this a bug?  Thanks.

...and some investigations of auto-save answered my question.  I lost my Empire plan bonus a couple turns ago :D  So a good little rule of thumb to account for costs increasing is check to see if you lost any bonuses (happiness/fervent would be one I could see happening a lot)