Why did you do your caluclation with Arca, and why not with Island. Island even has better liquidity for Nasaq stocks. They say Ecn fees also will be waived if you route to auoto routing. Now here depands all on their spped of excution, especially if they send to market makers and island for order flows then you might not get fast excution. IB has lot of services to offer, but they not cheap for heavy volume traders who trade over 4000 shares/lote. They have better plateform on their success trade site. Low trade web plateforms look like Datek Direct. I am with point direx for 0.75cents all in all. For 500 shars/lote =$3.75 They will give me better rate, if i trade volume.
nana, just to clarify.... using your example of your rates, IB is cheaper by $8+. IB doesn't pass on ECN or SEC fees. For size traders IB's fees approach .005 all in. Other firms may charge lower per share rates but add the SEC fees, savings on margin (IB's margin charges are usually significantly lower) and you pretty end up with a wash. Firms that cap their rates may offer a better deal but you need to be careful in regards to things like the costs for scaling in and out as well as the true costs of execution.(ie. if you limit yourself to one ECN then you might be giving up a penny here a penny there which of course is more costly than the commission.
Dunno if there was a problem with your math or maybe an ommision from the calculations, but for LowTrades you have total commision of $14 when it would actually be $20. (5+(3000*0.005)) In that circumstance, maybe Ameritrade is actually okay, since they allow direct routing to ISLAND (Note: Ameritrade, not freetrade) and they have a flat fee of $10.99 unlimited shares.... however This still probably isnt that great because they only allow routing to ISLAND and if you use their auto routing it's meant to make them commission $$$, not caring about giving the trader best price... but still, if they are subsidising big trades with the little ones it's fine by me. I've heard ISLAND is usually best bet as it's most liquid, but i'm no pro so someone enlighten me.