Low-income parents have a difficult choice at the start of every school year: clothes for their kids or school supplies, rent or school supplies and, in some cases, food or school supplies. Many families of these families can afford one or the other, but not both.

Those who earn less than $25,000 per year are 10 times more likely than high-income parents to apply for a new credit card in order to save as little as 5% on school supplies, according to a new survey from the personal-finance website WalletHub.

For those who can’t afford it, shopping for school supplies on credit is risky. Many credit cards, especially those marketed to low-income consumers, or to people with poor credit scores, charge interest rates as high as 30% or more, compared to the average credit card rate, which is 17%.

But they’re certainly not alone in putting school supplies on credit. Some 87% of Americans plan to pay off their back-to-school purchases before the end of the year, but others may need longer than that, according to a separate survey by CardRates.com, a credit-card website.

School supply shopping is expensive: Families with children in elementary through high school plan to spend an average of $684.79, according to the National Retail Federation, a trade group. Families with children from kindergarten to college age will spend $82.8 billion on back-to-school shopping this year, down slightly from $83.6 billion in 2017.

High-income families are also 3.7 times more likely to do their back-to-school shopping on Amazon.com than low-income families, the WalletHub survey found, possibly because Amazon AMZN, -0.25% charges money to ship those items, unless they are members of Amazon Prime, which costs $119 per year.

Low-income families may be able to find local organizations that provide donated school supplies. United Way, a nonprofit, holds a school supply drive every summer at many locations across the country.

Some 83% of the children who received school supplies from United Way in the Fargo, N.D., area were also on a free or reduced-lunch program, said Lisa Bowman, chief marketing officer at United Way.

One problem: If schools struggle with funding, it’s up to the parents to step in or, in some cases, even the teachers, she said. “Truly being prepared and having what you need removes a barrier to learning,” Bowman added.

Kids in Need Foundation, a nonprofit based in Dayton, Ohio, gives free school supplies to teachers and their students, at centers around the country. (Parents can find a center near them on the Kids in Need Foundation website). The Salvation Army and Boys & Girls Clubs of America also have their own school supply programs.

“When families have to make decisions such as putting food on the table or paying the rent, it often means their children’s backpacks are empty,” said Renay Dossman, Kids in Need Foundation’s executive director.