My estimate came to around $22k/kilometer for the cable itself plus the laying it in deep ocean. I didn't estimate the costs of repeaters.

The Google project was $33k/kilometer, so I don't think I could have been too far off on the cable itself. Looking at other undersea fiber projects, that seem about typical. For example, this one [2] estimated $27k/kilometer [1].

Here's an Alibaba seller with submarine fiber for $2000-9000/kilometer [2].

The submarine cables have an aluminum or copper tube around the fiber optics, an aluminum water barrier, and a sheath of stranded steel wires, and an outer polyetylene layer, with various other layers of mylar, polycarbonate, and petroleum jelly in between.

I'd expect the metal layers to be the most expensive parts. Looking at the cost of tubes or cables of those materials, it looks like each of those would be in the $1000-2000/kilometer range.

[1] http://infrastructureafrica.opendataforafrica.org/ettzplb/co...

[2] https://www.alibaba.com/product-detail/Submarine-Fiber-Optic...

This's so freaking cool!

10x is a fair estimate of cost vs regular armored fiber cable.

Source: I've laid subsea cable.

Just to be sure, you mean 10x between subsea cable and regular armored fiber cable, not cat6 I can get from best buy.

Yes, not that there's a large difference. Best Buy has pretty large markups, especially on short CAT6 cables.

You can buy subsea cable for $10-$20 per meter.

EDIT: the cost depends on how many layers of armoring you require. Deep sea cable requires less, shallow sea cable more.