Every society faces​ trade-offs because we live in a world of scarcity. Suppose a​ student-athlete has the opportunity to earn ​$400 comma 000 next year playing for a minor league baseball​ team, ​$700 comma 000 next year playing for a European professional football​ team, or​ $0 returning to college for another year. The opportunity cost of the​ student-athlete returning to college next year is ​$ _______. ​(Enter your response as an​ integer.)