Android and iOSMobile App integrated with Odoo special built module (Don't bid if you don't know Odoo)

We are looking to create a mobile App that is integrated with a special built Odoo module. When Mobile has data, the App should exchange information to Odoo. It should work as well perfectly offline and store data, to send after when online. Scope is to understand the Odoo module already created, build the API with Odoo purpose built module and then create the Mobile App. We will start with the Android App but need to understand the total cost including iOS. Please note that the budget for the project is in hundreds and not in thousands. It shouldn't take few months but few weeks. We don't want to go through a painful process and find out we are not speaking the same language when it comes to budget.