How much is Twitter selling its users for? An email from the company to potential advertisers has revealed the apparent value of followers, with the rate for cost-per-follower estimated at between $2.50 and $4.00 (cost-per-engagement, which includes retweets, favorites and click-throughs, runs from 75 cents to $2.50). Twitter requests that advertisers signing up with the company have a minimum $15,000 buy-in for a three month period.
