Its cheaper because the differences in height/pressure between both ends would push the cargo on its own. It would be similar to drooping an object from height

Its cheaper because the differences in height/pressure between both ends would push the cargo on its own. It would be similar to drooping an object from height - when gravity works you don't need extra energy to push the object. You wont reach the floor. It would be suspended on simple "air bags" controlled by computer - again using the simple physics of gas in fluid being pushed upwards.