Hi, again, Carolyn. I took a quick look at Interactive Brokers and the pricing seems a bit high compared to Ameritrade, but it would be worth it if they have fast executions. For comparisons I calculated the cost of tradeing 5000 shares. At Interactive Brokers the cost comes to $27.50 where at Ameritrade it is a flat $11.99. That's more than double. But again, if they are fast and I can shave a tick here and there due to speed, it will more than pay for itself.
If you are a smaller share trader, though, IB can get you into 500 share for only $5.00, or a 1000 shares for only $7.50, which is almost half the price of the flat rate of $11.99 from Ameritrade.