One word. Rinko. Japanese technique for bringing full-size non-folding bike on trains. The techniques shown above are basically the same. Bicycling Quarterly did a detailed article on rinko, might show up in a search, and there are other articles online. Having said that, in shipping, as noted above, there are particular thresholds for increasing cost, and for a lot of things I have researched and found the sweet-spot in terms of volume/cost. But a diamond frame bike, wheels pulled off and on each side of the frame, fork removed, handlebars removed, seatpost removed, there's nothing you can do to make it smaller, so at that point it's a function of wheel size (diameter/height) and frame size (fore aft which stays more constant, and frame height based on frame size). Deflating the tires or removing can make the wheels smaller, but less armored.

The above discounts weight, but my guess is the volume and size limits are the critical factors.

Shippers should have a "bike rate", like the USPS has (had?) a "book rate". Don't you think?