Avatar and Tangled were both pioneers of new technology of course they were expensive, but there are amateur fan effects better than those from multi-million dollar movies and TV shows 15-20 years ago. And the games of 10-15 years ago can be made a couple of people on a shoestring budget. I expect that trend to continue.
>Makeup isn't going to be much cheaper just because you do it in Maya.
They won't use Maya. Technology progresses, and tools become easier to use. At some point in the future you'll be able to select an actor, click makeup and adjust some sliders.
>you still need an army of 3D artists
For original creations you do need artists (the tools will continue to improve and make each artist more efficient), but there will come a time when all you'll need to do is take a few photos of tree, or a building to make an ultra high quality 3d model of it.