A commodity sales system includes at least one server computer including a memory system, a commodity price specification module for receiving a purchase request of a selected commodity from the user computer and for specifying a commodity price of the selected commodity. A storage module that stores a component price table and a maximum/minimum price determination module are also included. A deduction setting module and a tentative quote setting module for setting the minimum price determined by the maximum/minimum price determination module to a tentative quote of the used personal computer are also included.