How much is a brand prepared to pay for followers?

The background (as of Dec 2012)

2006 founded, 100+ million active users per month, 50 million per day, over 250+ million tweets per day and currently 2,400 advertisers. Renewal of advertisers is 80% with 3 to 5% response – better than click through

The models

Cost Per Follower (CPF) : $2.50 to $4.00

Promoted Tweets: (PTw) : open to offers

Cost Per Engagement (CPE) $0.75- $2.50  [ where engagement = (Clicks + Favourites + Retweets + @Replies) / Impressions]

Worth 30 minutes - The Truth About How Twitter Is Making Money with chief revenue officer Adam Bain explains:
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