If you're doing 20K+ Monthly Recurring Revenue then you can go negotiate your fees down with a 3rd party or by yourself if you've got the time.  

If you're not doing 20K a month then you're time is best spent elsewhere!  

Trying to save a couple bucks moving from 3.9% to 2.1% is like hunting for squirrels!  Hunt yourself some elephants and grow your bottom line.