I am a Unity developer and use Vuforia SDK to build AR apps. I charge 45 USD per hour on custom projects and can implement any complex interaction required.
Here are more complex examples https://www.youtube.com/playlist?list=UUsrRBmm-ZzdeK59CUd_ZyFQ
To develop a basic AR application we need at least two items: an image target and a AR object. Image target is an image that will be tracked in the real environment, e.g. a business card, a road sign, a magazine cover. AR object is graphic 3D element that will be placed relative to image target.
AR object can be a 3D model, a video surface, a 3D animation etc. In more advanced situations, it can act interactively and depend on user behaviour and actions.