And that's just the costs, not counting the social good of a lot fewer sick people.
I don't get the impression that EPA shortchanged themselves counting savings. Table 13.1 shows 184,000 annual deaths avoided thanks to particulate matter reduction, each one valued at $4.8 million. That's a social good (a big one!) and over 21 years adds up to $18 trillion, the majority of the central estimate of savings if my math is correct.
The EPA report includes dollar estimates for improvements in IQ points in children, missed work days, restricted activity days, shortness of breath in children, "household soiling damage," visibility impairment, and agricultural yields.
I haven't gotten the feeling that they are exaggerating these (necessarily highly theoretical) numbers, but I do feel that they are counting whatever they can.