As with all things AWS, it depends. Yes EFS is 30¢ per GB and S3 is 2.3¢. But S3 also charges $5/million object writes (and 40¢ for reads), but EFS is "free"

As with all things AWS, it depends. Yes EFS is 30¢ per GB and S3 is 2.3¢. But S3 also charges $5/million object writes (and 40¢ for reads), but EFS is "free" (factoring burst capacity, per-instance maximum throughput limits, etc). Couple that with EFS' lifecycle migration allowing you to get storage costs as low as 2.5¢/GB for many write-once-read-(almost)never after 7 day applications, things get a lot more complicated.