Networking Solution

I need a solution. I have a router that broadcasts over a 1km range. I want to charge people for connecting to it. how would I go about this? I want to charge according to data transferred. for example they can buy 1GB for 1 dollar. after that they have to buy another bundle to continue browsing. Will i need to use mac address to know data transferred to a user or what exactly will i use. or maybe a downloadable app on mobile or windows to monitor data on the device itself and without it one cannot access the wifi? I need an expert in this