This is not to say that you can't invest lesser amounts with brokerage firms, but don't expect a great deal of individual attention to your portfolio unless you meet the firm's minimum requirements. When you purchase most mutual funds you are investing in many companies in several industries. Sector funds do not provide diversification because they concentrate in one industry, i.e., technology, health, energy, etc. Controlling capital gains taxes is one of the primary benefits of purchasing individual securities. There are minimum initial investments for mutual funds that may be beyond your means.
All mutual funds charge a management fee.
However mutual fund management fees can be substantially lower than those charged for managed accounts at brokerage houses.