DWDM per-wavelength costs are way, way lower than that, and, with the optional addition of encryption, perfectly secure and fast enough for disk replication for most storage farms. I've been there and done it.

Assuming that dark fiber is actually dark (without amplifiers/repeaters), I'd wonder how they'd justify the 4 orders of magnitude (99.99%!) profit margin on said fiber. That already includes one order of magnitude between the 12th-of-a-ribbon clad-fiber and opportunistically (when someone already digs the ground up) buried speed pipe with 144-core cable.

Google the term “high frequency trading”

So that's 5 million bucks for 50 miles? If there are other costs not being accounted for, like paying for the right-of-way that's one thing, but I would think big companies or in this case, a national government, could afford that bill.

Yeah, most large electronic finance companies do this. Lookup “the sniper in mahwah” for some dated but really interesting reading on this game.