It's a cute little story, but somebody in that family needs to brush up on their math skills. Example: Let's say their car only gets 10 miles per gallon, so they walk to save money. If we figure that the average walking speed is 2 miles per hour, that means it takes 5 hours to walk 10 miles. If we also figure that gas is $2.50 per gallon, they save $0.50 per every hour they walk. Even if you walked for 8 hours straight, you would only save $4.00. Do I really need to go on?
And they're going to be thirsty, so you'll need to factor in a couple bottles of water.