Since Cost Calculator version 2.2.4, once you install and activate plugin (or just update plugin to that version if you had it previously), a new option, Product License, will appear in Cost Calculator panel.
Once you enter Cost Calculator's purchase code you will be able to receive notifications about new plugin versions, and update it through your dashboard, in Updates panel.
Please note that you are not required to enter purchase code in order for the plugin to work. Registration with purchase code is only used to receive plugin updates through wp-admin panel.