It's unclear exactly how Mattel calculates "Media Impressions", but the claims regarding them are often pretty unbelievable. After the Barbies New Body campaign from a few years back, the company regularly touted a total of 5 billion media impressions associated with the Time magazine cover story and associated online and print media coverage.
5 billion media impressions, in a world with a total population of 7.5 billion, out of which 3.5 billion have access to the internet. So according to that 5 billion number, every single person on Earth who has access to the internet saw that Barbie story plus an additional 1.5 billion people, who we can assume are so destitute they they don't have any means of getting online, also saw the Barbie's New Body story, I guess in the local paper or on TV or something.
To put this in a bit more perspective, the EU population is 750 million, the USA is 325 million, the entire continent of Africa is 1 billion. China, the most populated country on Earth is 1.3 billion. India, another 1.3. And even if every man, woman, child, baby, and geriatric, in EU, US, Africa, China and India all somehow saw this news about Barbie, you'd still be about 500,000,000 people short of the 5 billion claim made by Mattel.
To answer your question, generally a single ad click online is considered to be worth about .05 cents. Assuming people clicked through some link to read about the Barbie story, the impressions generated around the Time magazine cover and subsequent 5 billion media impressions would have cost Mattel around $250 million dollars if they were to have bought each view through traditional online ads.