You can see that they were buying terms like #JustinBieber to promote their own pages, for example. (This is the page the link clicked through to). Bidding oin terms is competitive, starting at $0.10 per engagement, where an engagement is defined as a retweet, a reply, a favourite or a click.
Read the post here, but the bottom line of their results in November and December was:
961,000 Tweet Impressions
Cost = $2067