I want to negotiate the price later so I have put any price. I want to develop a prototype app to show to potential clients before creating the real app. It should be a web app where people sign up with personal information. A master log-in would be able to register thing each people bought (like one beer for US$2.00). The mobile app would receive this information and show the information. Then then the user would pay, which for know will be only a click in a button and generate a qr code so a operator could read the payment information and act [url removed, login to view] mobile app would also send his wifi mac address retrieved by a router so the server could automatically recognize which user of this app is within the range.