The Smartest S&P 500 ETF to Buy With $500 Right Now

So you want to invest in the stock market, but you don't want to hand-pick specific stocks. Simply mirroring the S&P 500 (^GSPC -0.11%) market index can deliver fantastic results over the years, and you'll never lose a single night of sleep worrying about the rise or fall of any particular stock. But you're working with a strictly limited budget of $500 this month, and the usual exchange-traded funds (ETFs) are a little bit too pricey. Vanguard S&P 500 ETF (VOO -0.11%) traded at $549 per share on June 18. SPDR S&P 500 ETF (SPY -0.07%) costs $597 per stub, and the iShares Core S&P 500 ETF (IVV -0.11%) goes one tiny step further to $599. Sure, you can save up a bit more before buying these high-quality ETFs, or use the fractional share feature of your favorite stock brokerage to pick up 83% of an iShares or SPDR share for less than $500. But you actually have one more option. Meet the SPDR Portfolio S&P 500 ETF (SPLG -0.09%) -- a fourth pure-play S&P 500 index fund that costs just $70 per share today. How SPLG stacks up against the classics This fund is exactly the same thing as one of the classic S&P 500 index ETFs. They hold the same 503 stocks, reflecting the components of the S&P 500 index. The weightings are identical. Their management fees are slightly different, with an annual expense ratio of 0.09% for the more famous S&P 500 ETF and 0.02% with the lower-priced Portfolio fund. But both offer the same performance as the underlying S&P 500 index, for all intents and purposes: ^SPX data by YCharts The subtle differences that matter The SPDR fund managers at State Street (STT 1.04%) agree that these funds are very similar. They underline the fact that the higher-priced fund happens to be the largest and most heavily traded ETF on the market, making it the obvious choice when you're looking for top-notch liquidity. The bid-ask spreads are also lower for this fund, as a direct effect of the unbeatable liquidity and higher price -- bid-ask gaps a couple of pennies apart make a bigger percentage-based difference to a lower-priced ETF. With lower annual fees and higher price-spread trading costs, the Portfolio fund is arguably the superior choice for long-term holdings. On the other hand, the classic SPY ticker (or its VOO and IVV cousins) offers ever so slightly lower costs for more frequent trades. In other words, the ETF that's easier to trade with a smaller budget brings higher trading costs over time. It's the Sam Vimes "boots" theory of socio-economic unfairness at work. But there are a couple of awesome upsides this time. State Street makes up for the less efficient economics by charging lower management fees. And the resulting differences are incredibly small. Image source: Getty Images. Small budget, smart move All things considered, I think the Portfolio fund is a winning concept for people with modest investment budgets. For example, my daughter recently opened her first brokerage account with a SPDR Portfolio S&P 500 position that fit her budget just right. Fractional shares weren't an option, and it's probably better to get started quickly rather than saving up for a more expensive ETF. That position has already posted a double-digit percentage gain in less than three months, and she's off to a good start with a lifetime of intelligent money management. The SPDR Portfolio ETF may not be the perfect fund for your portfolio, and many investors clearly prefer the higher-priced version. But you should know about it, just in case this lower-priced option ever meets your specific needs. Today, $500 won't quite buy you a full-priced S&P 500 index fund, but you can get 7 SPDR Portfolio shares with that budget.