I'm pretty happy with the way I've resolved this. I publish everything to my personal blog first, then once a week I copy and paste it all into a Substack newsletter.
I get to use Substack for email distribution (which would cost me hundreds of dollars a month using most other solutions, I have 66,000 subscribers now) but my own blog stays the original point of truth.
Here's the tool I use for the copy-pasting: https://tools.simonwillison.net/blog-to-newsletter
Substack doesn't have an API for composing a newsletter, but their rich text editor DOES accept copy-pasted data - and copy-paste is the universal API.
This is super useful even if I just grab it as an idea to emulate. Have you used an agent to copy and paste for you ?
At 66,000 messages/week, you’d actually be spending around $50-$80 monthly with SES and a VPS + database for handling bounces and unsubscribe requests.
It's sort of disgusting that inbox clutter from a publishing service is the dominant delivery paradigm as opposed to browsers natively checking bookmarked RSS feeds.
You could do the same thing through Ghost, which has an API, and not be using a service that proudly platforms the Tates and nazis.