Title text:
It does come at the cost of some launchpad expansions and increased fuel requirements, but that all comes out of the facility's budget.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3291/
You need a bit less than 1/3 of it...
But it's supposed to be build in an ocean. Forests do not make for good logistics.
(It's also supposed to use a series of hypersonic iron pellets running inside a tube, that will explode and endanger a hundreds of km radius if something like even an air leak appears there... So yeah, the size is the least of the issues here.)