KRISTEN BARNETT, a high school sophomore in Sherborn, Mass., hoped to multitask this summer, combining outdoor adventure and Spanish-language practice with meeting her school’s community service requirement. A volunteer tour to Costa Rica run by Global Works Travel fit the bill perfectly. But the price — more than $4,500 — did not. “We’re more nervous than we have been in the past” about finances, said Leslie Barnett, Kristen’s mother, who owns a small business and whose husband works in software.

The solution? Kristen will cover half the fee with baby-sitting, refereeing youth soccer and cash from her grandmother, while her parents will stint on upkeep. “Our house needs to be painted, our driveway should be paved, and the cars need work,

Ms. Barnett said. “We are really