everything old is new again
Compare and contrast: CPM comes from traditional advertising - web guys call it 'cost per click' because there is no Nielsen verification but CPM for broadcast network television in the United States is between $15 and $30. Reddit's ads are paltry cheap by comparison, probably because they're thunderously ineffective. I can't remember who calculated it but the click rate on banner ads is like 0.06%, and it's estimated that half of that number is accidental.
But then, that's what you get when you aren't targeting for shit. If I buy Facebook ads I can target college-educated women between 25 and 35 within a 5-mile radius of my business. My CPM is closer to $10. Or I can go Yelp - I can target people searching for "midwife" and pay $10 per click.
And neither f'n one of them are half as effective as a little SEO 101. The economics of the Internet 101 right there: 4 hours following Google's guides on page rank are more effective for my business than a years' worth of Facebook ads at $200 a month... and that 4 hours is about as effective as a big fuckin' sign on the corner.