The difference between one that falls into the ocean and one that brings itself back down into orbit and lands safely is one is cheaper than the other?
I guess the better analogy is "an orbit is an orbit". We don't care about the orbit as much as we care about the rockets in the case of SpaceX, because what the rockets mean for our ability to explore space.
In the case of Boring, a tunnel is a tunnel, but if they can make them cheap and fast, that opens up a bunch of possibilities for improving transit.
With SpaceX, it's very clear how they're getting the >10X cost efficiencies. Rockets are massively expensive to build, and instead of building a new one for each launch and throwing them away as part of the mission, SpaceX is reusing each rocket many times. Their next-gen architecture BFR will be reusable dozens of times. So it's super obvious how SpaceX is putting things into orbit cheaply.
This is not true at all for tunnel construction, though. SpaceX is using largely the same technology (tunnel-boring machines) and is going to have all the same problems going through permitting, land acquisition, entrance/exit construction, etc., same as anyone else. It's not clear at all what fundamental advantage they have that would allow them to do this stuff much more cheaply.
