Ghost World
It cost him fifty-thousand system points to amplify The Green Plague ability! It was expensive, because the power itself was one of a kind, for a start, but also, it was a new ability that had never been amplified before! The cost wasn't light, but he had to pay for it.
The second thing that made it so expensive, was the fact that he amplified it by thirty-percent, rather than his usual twenty! This bumped up the price of the amplification process significantly, but he was enthralled to do so, because it was simply too expensive to use this ability otherwise! With a thirty-percent decrease of mana usage, The Green Plague ability would take seventeen-thousand five-hundred mana points per second to be used, at most, which certainly was cheaper than twenty-five thousand!