Many of the top ETF index funds that follow the S&P 500 have costs under 0.1%, meaning they cost $10 for every $10,000 invested. But investors don’t have to stick with broader market to find the best index funds, since many sector and niche funds are available at cheap prices. Here are nine top low-cost index funds. A total stock market index fund is a mutual fund or exchange-traded fund (ETF) that invests in a basket of stocks that passively tracks the performance of a broad stock market benchmark, such as the Wilshire 5000, the CRSP US Total Market Index, Russell 3000, or the Dow Jones U.S. Total Stock Index. The S&P 500 index fund continues to be among the most popular index funds. S&P 500 funds offer a good return over time, they’re diversified and they’re about as low risk as stock investing gets.