Just to give an idea. The best rate I have got on clearing with GSEC trading with REDI+ was 0.0035 per share + you all the fees, no minimum per trade. But bear in mind that I was looking for options trading, so I didnt promised too much of equity trading. Subject to 1 M account and 2.5K commission a month. About the same you can get with Merrill.
But standard rate starts 1-1.5 penny per share. That includes access to the dark pools, but not all algos.