Ask TheStreet: So Many ETFs

You may be willing to pay more for an ETF if you believe it will make up for the costs in performance, but once again, you have to really do your homework to make sure you know what you're getting.

Looking at the financial sector again, XLF and VFH are both based on market-cap-weighted indices that primarily track domestic financial stocks. And their expenses are very similar -- 0.24% for XLF and 0.26% for VFH. However, IXG, because it includes a high percentage of international stocks, charges 0.48%.

And some products carry even higher expenses. For instance, the PowerShares FTSE RAFI Financials Sector Portfolio tracks an index that weights financial stocks based on fundamental measures such as sales, cash flow, book value and dividends. Because of this more complex weighting methodology, the fund charges up to 0.60%.

In addition to expense ratios, you should also look at bid-ask spreads (which could be affected by liquidity), because they can add to your costs.

There are many Web sites, such as Morningstar.com, that provide information and tools that can help you compare different products. But if you can't find what you're looking for there, check out the ETF companies' Web sites, where you should be able to locate the necessary information.