Sending emails is an important part of any website for marketing or transactional tasks, but it isn't free.
You have to pay for a domain name, an email server, and software to use it and make the most of it: the bill quickly becomes expensive as you scale.
To send 30,000 emails, you'd need to pay at least $40 per month using Mailchimp or $10 monthly with Mailjet, for example. There are tons of alternatives with different features of course, but those two can give you an idea of the global price range of multi-purpose email marketing platforms.
As of today, Cowriters runs on a barebone solution using Amazon's Simple Email Service. It's the cheapest software solution out there, at $3 for 30,000 emails ($0.0001 per email, and 62k free emails if you have a web server hosted by Amazon). You have to code almost everything yourself, but it's no doubt the best way for me to send automated emails for my apps: just one API request and off I go.
I don't care about tracking what my users do with my emails, so I have no need for fancy analytics. I know how to write in HTML, so I don't need a fancy text editor either.
On the other hand, email hosting and web hosting are the two main running costs for me as an app developer, so having full control over these bills is non-negligible if I need to scale.
The only way to reduce my recurring costs even further would be to invest in my own server, but it isn't an easy thing to do. Sysadmin is a full-time job after all, and you can't afford to make mistakes when your app is in production. Even more so when a single error could lead your IP address or domain name to be blacklisted, and thus become unusable.
Still, there is probably a niche for a dead-simple email provider with a focus on privacy, cost-efficiency, and a minimalist interface. We had several issues with Mailjet when it comes to usability at Sipreads: slow text editor, 200 emails per day limit, emails not being delivered... With 3000+ subscribers, I might need to investigate for an alternative solution.