> S3 Express One Zone delivers data access speed up to 10x faster and request costs up to 50% lower than S3 Standard [0]
The critical difference seems to be in availability (1 AZ)
[0] https://aws.amazon.com/s3/storage-classes/express-one-zone/
Egress and storage however are more expensive on express one than any other tier. For comparison, glacier (instant), standard and express are $0.004, $0.023 and $0.16 per GB. Although slight, standard tier also receives additional discounts above 50 TB.
The house always wins https://www.vantage.sh/blog/amazon-s3-express-one-zone