$1.5 per 1K emails include Custom DKIM? If yes, then it is really a great deal.
http://support.sendgrid.com/entries/98008-how-to-eliminate-t...
Also, do you support mass newsletters sending to subscribed users? I use sendgrid because many other providers like MailChimp said they don't allow it.
To be fair, sendgrid's service is also very good, e.g. customer support, reliability etc.
We do not allow newsletter (or any bulk style) sending - I explained our reasoning behind separating and only sending transactional email through Postmark - by definition of transactional, the recipient is expecting the email and it is a custom response to an action.
Edit: typo.