Other than spammers, who is concerned about sending email newsletters cheaper? Your service looks like a great tool, but I'd encourage you to ask your early users why they like using you. I'd guess that "It's cheaper than mailchimp" won't be the answer you hear.
+ You don't really want to tout yourself as the low-cost-option. You have nowhere to go but down.
+ You don't really want to tout yourself as the low-cost-option. You have nowhere to go but down.