We run newsletters on Campaign Monitor and Mailchimp, and either is fine for a small business. Setting one up properly means a template that looks like the rest of your business, a sign-up that actually appears where customers might use it, and the technical groundwork that stops the whole thing landing in junk folders.
That last part is worth dwelling on, because a newsletter that goes to the junk folder has cost you exactly as much to produce as one that arrives. Mail providers now judge whether a sender can be trusted, and the records that prove your mail is genuinely yours have to be right before the first send rather than after somebody notices the figures are poor.