You might think that all stock index funds would have rock-bottom expenses after all, similar index funds basically own the same basket of stocks. And yet the expenses for S&P 500 index funds can range from 0.1 percent of assets, or just $10 per $10,000 invested, up past 2 percent. Stranger still: Consumers last year increased their investments in the more expensive index funds at a faster rate than they did the cheap ones, according to Tom Roseen, a senior research analyst at Lipper.

Why are investors shooting themselves in the wallet? The expensive funds are pricier in part because they re sold through financial advisers, a portion of whose compensation is built into the funds fees and a lot of advisers saw their business tick up during the crash. Many investors made a conscious decision to pay for advice, Roseen says.

There s another reason adviser-sold funds tend to be expensive: Most are too small to get the economies of scale that keep fees low at huge funds from providers like Fidelity or Vanguard. Mercer Bullard, president of Fund Democracy, a shareholder advocacy group, says these smaller funds can get caught in a vicious circle; their expenses chase potential customers away, so the funds stay small and expensive. Occasionally, a fund company will throw in the towel. UBS recently liquidated an S&P 500 index fund with annual expenses of 1.45 percent, among the highest in the category. The fund became increasingly difficult to manage for shareholders in a cost-effective manner, says a UBS spokesperson.

Rydex SGI has the most expensive S&P 500 fund on the market today; its no-load, adviser-sold shares cost 2.3 percent annually, three times the average for S&P 500 index funds. A spokesperson for Rydex says this isn t comparing apples to apples many investors use it as a trading vehicle, she says, because unlike competing funds, it doesn t have a minimum holding period and is priced twice a day instead of once.

That s not much consolation for buy-and-hold types, but such investors have options if they get saddled with high-cost funds. Bullard says clients should ask exactly how much of any fund expenses are going to their adviser. And investors can always do their index investing on their own.