Earlier quoted context omitted.
10x Supermicro SSG-6049P-E1CR60H servers (60 x 3,5" HDD in 4U enclosure) - $5k each 600x WESTERN DIGITAL Ultrastar DC HC550 18TB (10800PB in total) - $500 each ~$350k in hardware, up to 20kW energy consumption, should fit in two rack towers. You can host it for about $1.5k somewhere. All assuming no redundancy :)
Don’t forget labor. You need to find talent to manage your little data center. And deal with it when it shits the bed at 4:12am on Christmas morning. So toss in at least one SRE type person. Say $200k/year. Since you only have one, they are gonna be on call 24/7, so assume you’ll burn them out after a year and a half and need to hire a new one.... Since redundancy is a thing, double that $350k. And 10pb is what they…
Also, the hardware can be depreciated, which reduces its net (of taxes) cost dramatically over time.
Five years (probably the useful life of the equipment in general) of $210,000 per month is $12.6M. That's a lot of savings.