Received: 18 October 2017
Accepted: 5 August 2019
First Online: 16 August 2019
Ethics approval and consent to participate
: The study has been granted ethical approval from the University of KwaZulu-Natal Humanities and Social Sciences Research Ethics Committee, Ethics.number: HSS/0154/013.
: Not applicable as data was sourced from price data files.
: The authors declare that they have no competing interests.