You can use your own domain or sub-domain with DirectoryKnowledgebase! There is no extra cost for doing this.
To set this up go to the Settings Section then Custom Domains. Enter your custom domain and you will be given instructions on how to verify domain control/ownership and set up your DNS. We can host on SSL too and we'll automatically generate a secure certificate for you. Once again, there is no extra cost for doing this!
Once you have set up your custom domain or sub-domain both that and your original subdomain URL will work and serve content. If you don't want the original default domains to work just select the redirect option and any traffic will be redirected.