Once your Mailchimp account has been created, you can follow the directions in this article on how to integrate it with Member Essentials: Setting Up the Mailchimp Integration
Member Essentials has an integration with Mailchimp, a bulk email software that offers a free plan with up to 2,000 contacts. Click here for more details.
Also, Mailchimp offers a 15% discount to nonprofits and charities. To request the discount, sign up for a free account, and contact their Billing team with your username and a link to your organization’s website. They have a variety of plans listed here: https://mailchimp.com/pricing/