Prolonging a network lifetime is one of crucial issues of message routing protocol in mobile ad-hoc networks (MANETs), because MANETs consist of mobile devices powered by batteries. Previous routing protocols focus on route selection by a message sender to balance message forwarding load. However, in this approach, message routes determined by different senders cannot be coordinated, because each sender selects its message route independently. In this paper, we propose an auction-based route allocation scheme where message routes are determined by auctions between message senders and forwarders, and apply the route allocation scheme to the Dynamic Source Routing protocol. Simulation results show the DSR protocol with our allocation scheme can prolong the network lifetime comparing with the routing protocol proposed in the previous works.