Yuri,
For that amount of storage that I strongly suggest using Legacy format backups as it will save you a tremendous amount of space. With Legacy format, once you backup a file, it never gets backed up again unless it is changed which is rare for videos/pictures.
I would recommend Google Archive or Coldline. The cost per month for Archive is $.0012/GB/Mo in the cheapest Google regions (US-Central,East1,East5,South1,West1). That is 70% less than the $.004/GB/Mo for Coldline in the same regions. The data is required to be retained for 365 days but in your case that is not an issue.
5TB of data in Archive is a mere $6 per month vs $20/Mo with Coldline.
The issue that I am not clear on is how much the initial upload wil cost to each of the destinations for Class A and B API operations. It might cost a lot more in API ops to upload the data to Archive vs Coldline such that it might take a long time to break even using Archive storage.
Perhaps someone more knowledgable of API costs can weigh in.

Disregard my previous statement - I just learned that Google Archive is not currently supported. Changing recommendation to go with Wasabi or BackBlaze as they do not charge API fees. So while they MAY be more expensive than Google Coldlne (depending on the region you select), the absence of API fees will offset most if not all of the difference.