Looking for an App builder(s)

My company resells dietary supplements directly from manufacturer and we would like to have an app for our customers to use, I was looking at either getting multiple freelancers/VA's to work on different aspects of the app so that no one person would bottle neck the process or get a single entity to do it...which worries me if they try to upcharge as the project progresses...:/ If anyone has experience with this let me know! I'm just trying to find the most economical route possible