Seems high.
You can get a spinning disk of 18TB (not need for SSD if you can parallel write) for 224€. Let's round that to $300 for easy calculations.
To store 100 petabytes of data by purchasing disks yourself, you would need approximately 5556 18TB hard drives totaling $1,666,800.
Of course, you'll pay more than the disks.
Let's add the cost of 93 enclosures at $3,000 each ($279,000), and accounting for controllers, network equipment ($100,000), and power and cooling infrastructure ($50,000, although it's probably already cool where they will host the thing), that would be a about $2.1 M.
That's total, and that's for the uncompressed data.
You would need 3 times that for redundancy, but it would still be 40% cheaper over 5 years, not to mention I used retail price. With their purchasing power they can get a big discount.
Now, you do have the cost of having a team to maintain the whole thing but they likely have their own data center anyway if they go that route.