Your numbers are basically fine for what you're measuring, if you round up to factor in actually having servers to put the storage drives into. So 40-50k instead of 36k.

The issue is your budget is for 400TB of data but minimal requests per second. That's a valid thing to consider, but it's extremely apples and oranges to a fleet of 75 high powered servers.

To put it a different way, their prices are pretty high but the calculation of powerful servers costing 40x as much as raw storage isn't "insane".