I just don't see how this is possible. Most journals have volunteer editors, that need to find and send the article to volunteer peer reviewers all by themselves. I don't see how that would cost anything at all. At most, there is software that handles all of this, but there are numerous competing companies that offer complete off the shelf already hosted solutions for this, so I really doubt this software costs more than $10 per paper. Most journals seem to use Aries Editorial Manager, which doesn't list prices online.

It's hard for me to see what journals are actually doing or offering other than web hosting, the $6300 seems like just rent seeking with the journals name.