You can also think of adding a pay per use. Since you are talking to a price conscious audience (the non price conscious ones are already using MailChimp). Maybe $5 per use (unlimited mails).
I think your right the initial entry is a bit steep. The thing that scared the crap out of us with mailchimp was that there was no end in sight for price increases. If they had a max of $500 then we may have stayed on mailchimp. I guess our thought process was if you start with us you'll never leave because our prices will top out. But yes I think we'll introduce $5 for the first 1000 to get you going something like that maybe?
Pay per use is a difficult one, I think once you start complecting the pricing model like that people don't know where they stand. Personally I prefer simple.