Cain and Zen Corp. orally agreed that Zen would specially manufacture a machine for Cain at a price of $40,000. After Zen completed the work at a cost of $30,000, Cain notified Zen that it no longer needed the machine. Zen is holding the machine for Cain and has requested payment from Cain. Despite making reasonable efforts, Zen has been unable to resell the machine for any price. Zen has incurred warehouse fees of $500 for storing the machine. If Cain refuses to pay Zen and Zen sues Cain, the most Zen will be entitled to recover is ??