When you license a domain for Total CMS, there are no recurring costs. It is a one time fee for each domain that you register.
A license is good for a domain and its sub-domains. For example, joeworkman.net and subdomain.joeworkman.net can be used with a single license.
Use of licenses on subdomains are meant for testing purposes only. You must acquire a new license if a subdomain is not to be used for testing or development purposes.