Hi,
To integrate mapbox into unity will take approx 1 hour, it's pretty simple to do and there are detailed instruction on how to do it on the mapbox developer portal, of course I doubt that's all you require as ok it will be integrated with unity but apart from showing a map, won't do very much else.
If that is all you need then I would only charge 30$ to do this.
If you want more than that, as I suspect you need at least some functionality behind the application you want to build, please open a chat with me and we can discuss your exact requirements and I can give you a solid price for the work involved. In any case even if you don''t end up hiring me, I'd be happy to give free advice.
A little about me, I'm an expert in Unity with a specific focus on map based applications, I'm equally proficient working with open street map, mapbox and google maps, and as such already know the holes and pitfalls to avoid and exactly what is possible and realistic to be developed around these technologies.
All the best
Chris