The minimum investment varies from one ETF to another. For instance, the SPDR S&P 500 ETF (SPY) traded at about $377 per share as of June 30, 2022. Buying a single share used to be the minimum investment to participate in an ETF. However, some online brokers and investment apps now let you trade in fractional shares, which allows you to begin investing with as little as $1, or even less in some cases.