In the long run, it's always going to be higher than what companies dealing with storage services. First, because of effects of scale, second, because of the overhead of dealing with the crypto layer / extra network costs.

Possible but doubtful. Check market price history - the overheads of dealing with crypto are historically tiny compared to the profits of being forced to hold any.

At time of writing storing a TB for a month is ~10 usd. That looks to be cheaper than s3

S3 does a 1000 things on top of data storage. It will always be a more expensive option to compare to. Try wasabi as mentioned or backblaze B2.

Wasabi is 5$ per TB and month.