Most ETFs carry a fixed basket of securities and are typically created to match an index, or particular category of stocks, allowing investors to access a portfolio of equities focused on a broad or narrow cross-section of stocks. Some investors may be asking how low commissions can go. Free is about as low as it gets. Maybe big financial-services companies will ultimately do away with commissions and charge only a small annual fee, recognizing the value of assets held in their accounts. Or maybe this price war will result in a draw -- much as airlines realize they can only cut fares so much without becoming unprofitable. For retail traders, this promises to be an interesting opportunity to either day trade or build a balanced portfolio at a low cost.