My first guess is ESP pricing. Just to pull numbers out of thin air to anchor the conversation, mailing to 20,000 subscribers costs $200–$400/mo at Mailchimp/ConvertKit/Klaviyo, three of the top choices in the space. If it's 50,000 subscribers, that's $380–$800/mo.
Just playing devils advocate, but why not just switch to posting on a free hosted blog platform? The information can be there for all to see, it doesnt need to be distributed directly into mailboxes by premium mailer services.
You can send emails for free if you don't use some bullshit platform, no?
These are email marketing platforms, not bulk transaction email platforms, and I don't see why they can't do with the latter. At a bulk transaction platform, such a tiny amount would cost at most $20-$50/mo. If you're willing to do a bit of work to use AWS SES, that would be $2-$5 a month. Azure ACS would be even cheaper.