Whats a way, or ways, to move an object in and out of the line of sight (using a motor)?

I need to move an object into and out of the line of sight so the system can perform 2 different functions (1 function when its in the line of sight, and one when it has been removed from the line of sight). I need to use a motor to do so. Also it must be a highly repeatable process (thousandth of an inch from its original position). The object is rigid and cannot take on any deformation. There are objects relatively close by that could help as a foundation, if a mechanical arm were implemented.

The whole system is in a small scale. The object is lightweight, somewhere around a few ounces is my guess. The motion operation does not need to be all that fast, although it wouldn't hurt if it were. I'm only worried about whether the mechanism can do the process at this point, I can worry about speed later. TRANSLATIONAL motion of the object would be best. This way tolerances have a better chance to be maintained.

I'm attempting to minimize cost and be very efficient at the same time. Any help would be greatly appreciated!!