For the source, see [1]. "The coverage gap– those living outside of areas covered by mobile broadband networks4–continues to decrease below the 1 billion threshold and now stands at 750 million people. Since 2014 the gap has more than halved, from 24% to 10% of the global population." It's actually 90% covered by 3G and 4G.

Regarding the costs, I am not sure where your 60k/sat is coming form. Currently, launch costs for SpaceX are in the millions (60 commercially, let's say 30 millions cost), and they are launching 60 satellites at a time, so at least 500k/sat.

I am not sure that they will be able to cut the launch costs by a factor of 10, even considering resusability, larger launch capacity, etc, etc.

[1] https://www.gsma.com/mobilefordevelopment/wp-content/uploads...