Sendy has worked perfectly for us. The UI could do with a lot of love, but its functionally fine.
It has a built-in delivery service, but can also plug into SES or any other SMTP service for a one-time fee.
[1] I am a developer of the aforementioned app
There is no real difference in cost to the transactions themselves (to an extent, and in this example). You are willing to pay to have the ability to transact, regardless of the size. The whole point here is that your 10K is more valuable than their 1K, therefore you would in theory pay more to have the ability to transact (regardless of # of transactions). I agree though - its gouging for no reason.
12.000 mails on Amazon SES are only slightly above 1$ (+ Sendy hosting of course). So the question is if Mailchimp offers features that save them 200$ worth of time.
It doesn't have the slick, "just works" appeal of MailChimp, but it also doesn't carry the big monthly price tag.
We've had the same open and clickthrough rates with Sendy as before, and I haven't encountered any problems getting marked as spam. That said, our entire list is people who actively came to the site and signed up for updates.
If price were no object, we'd go back to MailChimp in a heartbeat. But they were charging us $125/month just to keep our mailing list on the service, whether we sent anything that month or not. Just not a good use of funds for us at this stage. Sendy is great at our current size.