I know that espionage costs are associated with the slider and other factors. But the one question that I cannot remember the answer to is:

Does it cost more to perform an act of espionage during a war? It would seem to reason that all active missions would cost more during times of war because the other country would be on "higher" alert. I don't know if this is the case in the game or not (just cannot remember), but if not, that would be a nice addition I think.

No, but it does cost Less to do espionage with Open Borders