High investment costs remain out of sight and out of mind when overall returns are strong. Why sweat decimal points when basking in 20 percent gains?

But when returns turn meager or slide downward, as they have in 2008, hefty expenses become visible and painful.

While investors can find low-cost mutual funds, exchange-traded funds (ETFs) and bank accounts these days, it requires research and willingness to read fine print.

"Keeping investment expenses low was important a decade ago but now is critical," said Harold Evensky, certified financial planner with Evensky & Katz in Coral Gables, Fla. "You can't control markets, but you have some control over expenses and that is important in a low-return environment."

The sad reality is most investors pay no attention to expenses, Evensky said, including the fees they're paying on retirement accounts.

The average mutual fund's annual expense ratio had fallen from 1.00 percent to 0.90 percent from 2003 through 2006, according to Morningstar Inc.

However, it remained stagnant at 0.90 percent in 2007, and costs of some asset classes rose. Overall increases may be ahead.

The annual expense ratio represents recurring management fees as a percentage of fund assets. It includes managerial expenses, administrative costs, 12b-1 marketing fees and other operational expenses.

"Mutual fund expenses have flattened out — going down for international funds but up in other areas such as balanced (stock-and-bond) funds," said Russel Kinnel, director of mutual fund research for Morningstar in Chicago, who says too many investors put money in popular but high-cost funds. "There are a lot of different fund markets, some sensitive to fees and others indifferent to them."

International fund fees have gone down because their large asset inflows have driven down overall costs of running them, Kinnel explained. That's not the case with most domestic funds, whose outflows halted previous downward fee momentum.

"Some investors who buy mutual funds based on performance actually end up buying low-cost funds because low costs do contribute to better performance," observed Kinnel. "There are plenty of low-cost funds, but you must exert discipline in using their expense ratios as a good first screen on finding those that are low in cost."

Though not alone among fund companies with low costs, Vanguard Group remains the low-cost leader. Kinnel points to Vanguard Total Stock Market Fund Index (VTSMX), a "no-load" (no sales charge) fund. It features a low annual expense ratio of 0.15 percent, requires a $3,000 minimum initial investment and has a three-year annualized return of 9 percent.