So Christopher's "loss in value" is $20,000. His "other loss" is zero. Now we have to calculate the third element in our formula: "any cost or other loss that he has avoided by not having to perform."

What is Christopher's "cost avoided?" (Remember: Christopher whacked Jennifer and Tony welched on the last payment.)

 
He saved the price of some bullets.
 
He didn't avoid any cost because he fully performed his part of the deal.