Django REST-interface for mobile app

Looking to build the backend for a mobile application for multiple users to share media in well defined ways (similar to Instagram functionality). Current envisioned architecture (although open to change if better solutions are offered) is a Django backend communicating with mobile clients via REST-ful API. Authorization and authentication of users is required (oAuth2 or xAuth). JSON envisioned to be used to communicate between mobile clients and Django backend. Ability for mobile clients to change/share their media with other users of the service. Integration with Facebook OpenGraph API is optional and can be discussed in more detail. To summarize: 1) Django backend 2) Authentication/Authorization scheme to enforce user-desired privacy levels (and sharing). 3) REST interface between mobile clients and backend (based on authorization obtained in (2)) 4) Ability to upload and dynamically share media between users. If interested, please respond with rough estimate of time/price you think it will take/cost. This is not binding and we can discuss in more detail one-on-one. Thanks you