The Vanguard S&P 500 Growth ETF ( VOOG 0.03%) follows the S&P 500 Growth Index, which is made up of the 230 or so growth stocks in the S&P 500. That's less diversification than the benchmark index, but it's still a fair amount of stocks. It has an expense ratio of 0.1%, as compared with an average of 0.95% for similar ETFs.

S&P 500 on track for another year of 20%-plus returns. The benchmark index has produced total returns (including dividends) of nearly 25% as of this writing. On a total return basis, it has only had two years of negative returns since the financial crisis of 2008.

While not all ETFs are strong investments (and what you choose to buy will depend heavily on your risk tolerance and overall goals), there's one fund that could potentially turn $300 per month into $1.