3. Look for mutual funds with a low minimum-purchase requirement. Some mutual fund companies will allow investors to start investing with small deposits, but you'll have to agree to an automatic investment plan whereby you let them deduct a fixed amount from your bank account every month for the purpose of buying additional stock. Such investments can be as little as $25. You may also be asked to start off with a small one-time investment, sometimes as low as $25. As noted, this is an easy and relatively inexpensive way to build up a stock portfolio. ^[4] See How to Select a Mutual Fund.