You can always use the moodle paypal plugin. You may allow guests to see your front page. And restrict access to the actual courses using email-based self-registration and Paypal. Using the paypal plugin will allow you to charge for your courses. That way you do not have to do any emailing, or bother with enrolment keys. That is how I do it, because I don't want to do any work...that is what software is for...doing the jobs people don't want to do so that they can goof around.