Write a mobile application that functions as an ecommerce store

An existing website has been developed using Opencart for the sale of about 40000 products (books), and is well utilised. The requirement is to build a mobile app that uses all the features of Opencart and is synchronised to the Opencart database. The app must not be a mobile application 'wrapper' of the current website, this has been tried before and doesn't work according to the client's needs. The mobile application needs to meet the following requirements - • It needs to integrate with the Payfast payment gateway ([login to view URL]) • The client wishes to use the Opencart administration portal to update their products, categories & prices etc. Changes on the Opencart backend must reflect in the mobile application. • Upon signing up for the mobile application, customers need to choose where and what they are studying (the client sells schoolbooks) so the appropriate list of books (bundle) can be suggested to the customer. • Search within the app needs to be better than the Opencart website. • A custom UX / UI needs to be designed. • The app needs to be developed for both iOS and Android devices. • The app will need to be submitted to the Google Play and iOS store. Please provide cost estimates based on the requirements above, as well as a suggested timeline from start to finish.