I wonder how much it would be. I'm also curious what the post would look like. I'm guessing it's more about SEO, and less about clickthru. It's odd, so much effort goes into SEO, but I can't imagine that it really is worth the investment except when employed in aggregate.
Yeah it's SEO. Back links on sites help increase your google ranking. There is a PR (page ranking) number system for reputable to non reputable sites and each of these have an affect on your overall ranking on Google. If it's a really shit site that solely exists for backlinks it will actually hurt your ranking. My company actually got blacklisted from Google for a bit because they paid a Russian to throw up over 2000 backlinks on spam sites a few years back. Whoops.
Typically, for "legit" businesses, it is part of the SEO team's job. The girl we used to have would spend maybe 30 minutes in the morning linking on comments on related blogs, post to facebook/twitter/pinterest/etc, check on keywords, update budget for our Google Adwords and then move on to actual copywriting and research. If you do it enough I guess you can do it in your sleep. Dead links with awful copy, etc is probably something like Mechanical Turk or Fivrr though. For those it is literally pennies.Sometimes there are real folks dropping links in forums. They must get payed pennies per hour. It's awful.