I have Fidelity in my 401k which has $7.95 per trade. I sometime see an extra $.05 on a trade with a lot of shares, so they may charge a small fee for that.
I also have TDAMeritrade which has a flat $9.99 fee per trade. I used TDA because they had flat fees for options too. TDA redesigned their web site interface and I haven't used it much recently. I've heard complaints but people just don't like change.
I really like TDA's trading tools. They have the THINKORSWIM platform and also STRATEGY DESK to download and use.
You can do all types of scans and tests, and a whole slew of other things. People also "open source" their screener coding/formulas so you can get some good ideas that way. They'll show Level II, charting of course, and a whole slew of things.
I started writing a few simple screening formulas in the past week via THINKORSWIM. Am trying to have the computer find patterns that my eye/mind can see.
These thoughts are just mine, not right, not wrong, just thoughts. Invest in what you believe in, not what I believe in. Do your research, and invest in the facts.