Database: student_club
Question: Indicate the cost of posters for 'September Speaker' event.
SQL: SELECT T3.cost FROM event AS T1 INNER JOIN budget AS T2 ON T1.event_id = T2.link_to_event INNER JOIN expense AS T3 ON T2.budget_id = T3.link_to_budget WHERE T1.event_name = 'September Speaker' AND T3.expense_description = 'Posters'