A WordPress child theme is a theme that inherits the functionality of another theme, called the parent theme, and allows you to modify, or add to, the functionality of that parent theme.
ClassiPress is the parent theme and is required in order for you to be able to use a child theme, more explained
here. The child themes we have available for ClassiPress in the
AppThemes marketplace allow additional functionality or even just a different layout to the default ClassiPress theme. You could also
create your own child theme if you wanted to.
The subscription fee is optional, so you do not have to renew after the initial 12 months, however you would not receive further theme updates or support.
ClassiPress already includes an advanced search functionality which can be seen in the category sidebar as "Refine results" in the
ClassiPress demo site. There you can select the fields available based on your custom fields, including location related options. Thanks.