Just touched on this subject in another post.
The empty solids you are seeing on ebay are “samples”
That is they are lauder solids that never made it to Canada to be filled with perfume or boxed. These solids are being sold at a warehouse sale that Estee Lauder (in NY) has a couple of times a year, you must obtain a pass to go. There is no limit on what they will sell to you and from what people have told me they get them dirt cheap. The sellers with them on ebay have been selling them in the past and have just started selling them again.
They are making a small fortune on us collectors