Online judges in programming courses allow students to improve their coding abilities and instructors to analyze student work and detect challenging topics. Although several online judge platforms are available, most are limited in that they cannot support a large number of students simultaneously working on an assignment during a fixed time period, or can only do so at a significant cost, making the use of such systems in developing countries non-viable. This paper presents Clearn, a new platform that is (1) cost-conscious, as we have focused on lowering costs, (2) student-led, as we have empowered students and teaching assistants to lead its development and maintenance, and (3) highly simultaneous, as it allows over 1,000 students to work simultaneously on a timed assignment. This paper presents the platform, as well as the lessons learned during its development and deployment, and its reception by the students.