Write an mobile app ( IOS ans Android)

Hi, we are an agency and we serve small and medium business. One of our customers is interested in an application for your business, for remittances of money, usually from the US to Brazil. Like Xoom and TransferWise. In order for the user to log in, register the bank and credit / debit / paypal data and transfer to the account of another user, in Brazil, previously registered or informing the data of this user. In the physical office it works like this: the person delivers the money in the booth in the US, and the company, which has accounts opened in different banks in Brazil, transfers the equivalent amount, discounting a fee and of course, also make money with an exchange. I think the app would work the same way, the user transfers the money from his American credit / debit card to an American company account, as if it were a normal eCommerce purchase. Once the company's system receives this, a bank transfer transaction (manual or automatic) from the company account in Brazil to the payee account is performed. See that there is no international transfer in the process. This is done later by the company, on fixed dates and larger quantities, it would not involve the app. Anyway, tell me some considerations and follow the conversation. The application should be for iOS and Android. I would like to get a better idea of ​​costs and deadlines.