Google billing integration with xamarin android app and publish to google play store

I developed a project in xamarin android apps. I would like to integrate google billing and publish to play store. You have to finish two tasks. 1) Need to add code in my apps for billing. 2) I have google developer console. So, you need to add and publish. For billing purpose I need like My requriements : For example 20 user <= per month $5 50 user <= per month $10 100 user <= per month $15 300 user <= per month $20 500 user <= per month $25 1000 user <= per month $50 Like this . It also can go six month, yearly basis