There are a lot of regulations around commercial uses of email, so the best thing to do is use an outside vendor who specializes in this. This way, you’ll stay in compliance with the email regulations. Also, when sending mass emails, your regular email service may think you are engaging in SPAM and bounce the emails or shut down your service.
Services like Aweber or Constant Contact have well priced introductory programs to keep your costs down. The cost rises as your list expands.