Quote from luisHK:
I'm not sure about the execution, but with any volume in stocks, IB comes to a similar price in Europe
But than with an even larger volume and rebates, IB should become cheaper. Otherwise, from memory, at standard pricing, it's 0.1% commission or 29euros max per transaction in several european countries, and some countries without maximun commission .
More info :
http://www.interactivebrokers.com/en/p.php?f=commission