hum ... if espionnage works the way that other galciv2 abilities work then it should rather be :
-the Yor with +0 would spend, lets say 1,000bc when set at 25% spending
-the Kyrnn with their +50 would spend 1,500bc when set at 25% spending but would only really be charged for 1250bc (250 free bc added to calculations)
-the Iconians with their +100 would spend 2,000bc when set at 25% spending but would only really be charged for 1500bc (500 free bc)
That is: half the bonus is free of charge like for social production and all the others. well that's IF espionnage is in line with the general galciv2 way of dealing with bonuses
Ok, JUST started with a +espionage bonus and I have some interesting results already that may just show that this skill doesn't match the rest of the game's skills lol.
My income is 2020, I'm set on 4% espionage and have a +55% espionage skill (damned anomoly). 4% of my income should be 80bc, yet I'm spending 124bc. That extra 55% from my skill I'm still paying 100% of.
So, the skill does make you pay more, but that will help you get spies quicker since they have a set price.