@Edent Even though It looks like a huge expense the autonomy and sovereignty you need to be sending that amount of emails is well worth 300$/year! If you can't maybe Mailpoet can do the work... Although I think It will charge you after 1000 emails per month as well.
It would be good to see what do you pay to any other service that doesn't charge you money for letting you send those emails: data, user analysis, etc... so you don't become the product

@Edent What about some easy and nice plugin as The Newsletter Plugin and use a delivery email service as Mailgun? It can be 80 cents for a 1000 emails