Its becoming very clear just how low the cost of clearing a trade really is. IB offers a .005 rate all in - which is probably equivalent to a .004 rate with pass thrus at a prop firm. Many brokers are offering free commissions and making the money of interest. So dare I say it that at a prop firm if you're paying more than .004 then you're getting fleeced regardless of the volume you do. Keep in mind that your prop firm (whether a broker-dealer or a sub account) probably doesn't pay interest on your money and that's probably a major source of income for them aside from commissions.