The miles pile up on Stephanie Wiernik's Ford Ranger, and the math makes less and less sense.

For six years, Wiernik has been the rare violin teacher who traveled to students' homes to give lessons.

"I enjoy that, because it makes me more a part of their family culture," said Wiernik, 29, of Woodstock.

But with gas prices at record levels and still rising, Wiernik has concluded she has to make a change to make the job worthwhile —- raising fees or having students come to her are two options.

"It doesn't make sense, moneywise, to drive to people's houses," she said.

The bite of historically high fuel prices has snared even young violinists. Those reliant on their cars and trucks to make a living —- couriers, plumbers, mobile dog-groomers —- are making changes to stay afloat.

"It's costing me about $500 a day to run six trucks," said Jonathan Perez, owner of a Duluth air conditioning and heating service company. "It's a huge impact on our business."

Perez has made some difficult concessions to gas prices. Two weeks ago, he bumped up the cost of a service call from $55 —- the price it had been since he went to work for his father nine years ago —- to $65. While Perez's Cool Masters company prides itself on same-day service, dispatchers now wait a day or two until more calls arrive in the same area to cut down on trips.

Perez estimates that three out of 10 potential customers go elsewhere when they learn of the wait time.

Previously, fuel costs were not "a major factor in our overhead," Perez said. "Now, it's the first thing we have to think about."

At Marietta Dodge, the Sprinter cargo van has become an increasingly popular purchase. Business-link manager Don Garner said he has sold about 100 Sprinters, noted for their fuel efficiency, since January.

Among his customers is Superior Plumbing in Kennesaw, which says it is benefiting, relatively speaking, from its decision to switch its entire fleet of cargo vans to the Sprinter. Owner Jay Cunningham said the Sprinter gets about 20 miles per gallon, compared with about 10 mpg in the old vans.

"When you're using what feels like hundreds of gallons an hour, you want to look at that idea seriously," he said.

Fuel efficiency is a drain for Sonya Sanchez, a mobile dog-groomer. Her ambulance-sized truck putters along at 9 mpg, she said. The truck is saddled with 80 gallons of water, adding about 640 pounds.

She spends between $1,600 and $2,000 on gas monthly. Because of the extra costs, she says her assistants take home more money than she does.

In an Atlanta Journal-Constitution article in November 2006, Sanchez touted mobile businesses —- office supplies, veterinarians, car services and the like —- as the wave of the future. Now, she said, "I don't know how they're hanging on."

In a typical year, Georgia Messenger Service, a courier in the Doraville area, might raise rates once, possibly twice. However, because of gas increases, the company has already raised rates twice since January.

"We have a heart, too," said company Vice President Kenny Overby. "It hurts us to have to do it."

Wiernik knows all about it. Teaching the violin helped put her through college and has been her full-time job for five years. When considering raising her fees —- between $20 and $37.50 for a half-hour lesson —- she anguishes over squeezing out middle-class students.

But, with students spread out across Cobb and north Fulton counties, she doesn't think she has a choice as long as gas prices stay high.

At the end of the school year, she said, "I'm putting on my ruthless face."