Interestingly, DynamoDB is cheaper than S3 though, compared by number of requests. DynamoDB costs $1.25 per million write request units and $0.25 per million read request units. While S3 is $5 per million PUT requests and $0.4 per million GET requests.

Keep in mind that a write capacity unit in DDB is capped to 1kb. Writing a 10kb file to DDB? That's 10 write capacity units.

That's a good point, only very small data is cheaper in DynamoDB than S3. Also adding global secondary indexes tends to add cost, since writes are charged for each of them.