A slew of fees can quickly ding your prepaid debit card.

Fees may be charged for activation, withdrawals, overdrafts, paper statements, balance inquiries and even dormancy. For example, all 19 prepaid cards studied by Consumers Union charge fees for withdrawing cash from ATMs, ranging from 99 cents per withdrawal to $2.50.

But dormancy fees, or fees charged for nonuse of a card, are the most problematic, says Suzanne Martindale, an associate policy analyst at Consumers Union. "They would never happen with checking accounts," she says, adding that customer service fees can also add up.

The difficulty in computing card costs is in finding a fee schedule for prepaid debit cards, she says. "The packaging doesn't list them," Martindale says. "So you may find fees after the fact, unlike checking accounts."

Also, fees vary widely. So make a list of the ways you'll use the card -- such as online -- and compare fees for those transactions.

Still, some cards do carry low fees. The Mango Prepaid Card offered by Mango Financial Inc. has no hidden fees. Walmart's Moneycard also has simple fee schedules that are easy to understand.