You could try sendy (sendy.co) - self hosted with a one time cost. Worked well for us on a $5/month vps. The UI is not as slick as mailchimp and the composer is

You could try sendy (sendy.co) - self hosted with a one time cost. Worked well for us on a $5/month vps. The UI is not as slick as mailchimp and the composer isn't as good, but it works if your needs are simple.