Yep, the thing is they're using Fastly as CDN, moving 1.5PB a month, and its cost doesn't seem to be a problem for them (I don't know if its covered by Fastly or they have a good price). The gross of their problem is the storage, and S3 is probably the most expensive place to put raw storage.
If they start paying the bill, their best option is moving out. Either to a cheaper provider (be it R2, B2 or whatever) or self managing it (Minio...).
And seeing the $32K price for the migration to R2, and guessing that's transfer costs, I would garbage collect and move only hot data and let the rest be rebuilt during some months.