Just to be clear, it should be LESS expensive to use B2 in most cases. If you need less than 10 GBytes it is totally free in B2, but it is $5/month using the Backblaze Online Backup client. If you have 500 GBytes to backup, that is only $2.50/month using B2, but $5/month using the Backblaze Online Backup client. You break even at 1 TByte. And it costs you money if you have 2 TBytes to store.
Backblaze is not charging a premium for the B2 service. Let me put it this way: if somebody ELSE was willing to offer Backblaze storage at B2 prices we never would have built our own storage for the online Backup client. I'm not kidding. The only reason we had to build the storage layer is that to this day, Amazon S3 gouges customers at 4x what it actually costs them to provide the service. And don't even get me started at Amazon S3 downloads cost.
Backblaze Online Backup charges $5/month, and of that maybe $0.50 is profit (50 cents) living on the AVERAGES (make money on some customers, lose money on others). If it was based on Amazon S3 we would be losing $15.00/month by charging $5/month.