The distributed denial of service (DDoS) attack is detrimental to businesses and individuals as we are heavily relying on the Internet. Due to remarkable profits, crackers favor DDoS as cybersecurity weapons in attacking servers, computers, IoT devices, and even the entire Internet. Many current detection and mitigation solutions concentrate on specific technologies in combating DDoS, whereas the attacking expense and the cross-defender collaboration have not drawn enough attention. Under this circumstance, we revisit the DDoS attack and defense in terms of attacking cost and populations of both parties, proposing a joint defense framework to incur higher attacking expense in a grid of Internet service providers (ISPs), businesses, individuals, and third-party organizations (IoT Grid). Meanwhile, the defender's cost does not grow much during combats. The skyrocket of attacking expense discourages profit-driven attackers from launching further attacks effectively. The quantitative evaluation and experimental assessment reinforce the effectiveness of our framework.