2.1% of your budget for a single campaign of that size does seem like a reasonable tradeoff.
An intelligent brand manager has to weigh the positives and negatives of paid and earned media. In this case, in light of Saliterman's email, a brand manager would weigh the (seemingly high) possibility that the NRA would advertise alongside fearful messages from grieving families. Since Everytown knew that this was a possibility, the advertising alongside the editorial had the capacity to damage the brand and (perhaps more importantly) cost jobs.