Ask HN: Estimated costs to build a mobile app widget?

I'm curious as to the costs involved in building a fairly complex widget to be integrated into social (consumer) mobile apps. As an example, it would be like adding a "scoring" system option each of the app's tens of thousands to millions of users. Sorry in advance if this is vague, but I'm just looking for rough ranges. Basically, everything from hiring the developer/s to testing and launching.

Thank you!