In a mutual fund, there is scale. That is, buyers get volume discounts. For example, buying shares of One Eyed Man Mutual Fund Company's flagship fund, might cost 5.5% commission if you buy less than $25,000 worth. If you buy $500,000 worth of the fund, the commission might just be 1%. Over a million bucks, the commission might be free - the broker will be paid out of the management fee of the company, i.e. One Eyed.