I am looking for an expert programmers who is experience with Facebook APIs and Facebook app development. We would like to develop an app which will be downloaded on Facebook page without going on Facebook.
For example, seller create an store on Amazon/ eBay to sell their products. They will login via their Facebook account on the website, select Facebook page and install our app. Facebook App will be installed on their Facebook page and create a button like "Contact us" on the page. If any Facebook user click on the "Contact us" on facebook page of the seller, it will open the Amazon shop of that seller. So, when a seller install the app on their Facebook page, their shop link will be connected to the contact us button create on the Facebook page.
Please let me your estimated time and cost.