The single pricing option has been deprecated in the latest versions of the WP Travel plugin after version 4.0. So, this option is not available anymore.
However, if you want a single pricing option then multiple pricing options that are available in the latest version of the WP Travel plugin can also be used as a single pricing option. You can add only one pricing option with one price for one category so that multiple pricing options can act as a single pricing option.
Further, if you have any queries, please submit them to our Contact page.