The eleventh trade

"They say you can't get something for nothing, but nothing is all Sami has. When his grandfather's most-prized possession--a traditional Afghan instrument called a rebab--is stolen, Sami resolves to get it back. He finds it at a music store, but it costs $700, and Sami doesn't have even one penny. What he does have is a keychain that has caught the eye of his classmate. If he trades the keychain for something more valuable, could he keep trading until he has $700? Sami is about to find out"--Amazon.com.