But it's important to point out that 1) That $1.1 billion was for two facilities 2) LIGO underwent a huge upgrade over the last decade, making the instruments

But it's important to point out that 1) That $1.1 billion was for two facilities 2) LIGO underwent a huge upgrade over the last decade, making the instruments tremendously more sensitive, and the cost of this upgrade is included in there as well. So I suspect that building a third facility with the sensitivity of the two existing facilities would be a much more affordable endeavor. The first time around is always the most expensive.