Themoron,
What you've come across is a variation of a product commonly known as a True Image Projector (a.k.a. TIP or Epidiascope).
TIPs are used a lot in classrooms and for training where you want to show an enlarged image of some 3D object, e.g. a watch/remote control/circuit board. They work by reflecting light off the object and using a lens to magnify and focus it.
The plans for the version in the Ebay auction will probably use a portable TV as the light source set inside a sealed box, then magnify that image using a very large lens. It's the same principle as a CRT projector, but it won't be as bright and the sharpness very much depends on the quality (and cost) of the lens used.
The Ebay auction is only for the plans to make one, not the product itself. It doesn't include the cost of materails and your labour.
Regards