Perhaps look into Vast Data? They have a TCO calculator [1] but it seems to compare to other on-prem data storage providers (like Isolon...). 10PB in One Zone IA costs $100,000/mo without discount, or $1.2M per year, and that's just for storage alone. Vast claims something like $3.5M TCO over 5 years with 10PB of data and no growth assumption. 5 years on your S3 zone with no data growth (or transfer...) is $6M.

[1] https://vastdata.com/tco-calculator/