Why wouldn't they put all of that in a Backblaze Storage Pod? 2 months of AWS costs could've built more than 2 pods and stored everything with plenty of space to spare.
Price out the backup solution for that back blaze. Then make the backblaze geograohiclly redundant. Then write the system to keep them in sync. Then add versioning. Then pay for someone to manage it. Now you are getting towards the real cost of that backblaze to replace S3.