Talk to the other vendors. I know of a place that had about that same amount and decided to have a redundant copy of all of their data in another vendor's S3-compatible product. That vendor paid for all of their egress fees as long as they signed a 12-month contract and used their tool for the migration.
Mostly EC2 for data mining terabytes of historical data stored in S3. Production usage is fairly lightweight compared to the EC2 and S3 stuff. We did cut our bill a lot by moving to single AZ redundancy.
