We also switched from MailChimp to SendGrid, but it appears MailChimp will still be more expensive as they bill based on the number of "subscribers" instead of number of emails sent.
On MailChimp our cost is $210/month on SendGrid it is $100.
However, looking at their updated pricing, they also now have "Marketing" as a separate pricing tier, so I can't say exactly how that will affect us.
Also, I wouldn't value my time at $60/hr right now. When you're barely paying yourself in order to grow, hard to think of it that way ;)