You can bid whatever you want for followers. Twitter uses the same tactics as all auction-based advertisers and tries to tell you that you'll have to set prices

You can bid whatever you want for followers. Twitter uses the same tactics as all auction-based advertisers and tries to tell you that you'll have to set prices at $4 per action to see any results, when in reality they'll happily take your 30 cents per action if that's all you're willing to give them. There's no fixed price attached to action acquisition, so for these guys it's all about what you can get someone to pay, and you get them to pay more by telling them several times that they need to pay more to see results.