If you have one contact in two different Contact Lists, iContact counts that as two different contacts. Their subscriber plans are based on the number of contacts, not the number of messages you send per month.

I have several autoresponders going, depending on products purchased. As a result, my subscriber list is much larger than the actual number of contacts. Yet the number of messages I send out per month is actually small because I'm very targeted with my emails.

iContact should bill according to the number of messages sent per month, not the number of contacts. Else, they should charge by the number of individual contacts and ignore the repeats. It's the messages per month that drives expenses on their site, not the database of contacts, in my opinion. It's the number of messages that is a measure of how much I use their service.