cheap rate
noun [ C ] uk/ˈtʃiːp ˌreɪt/ us/ˈtʃiːp ˌreɪt/
（服务行业淡季的）促销价，优惠价，便宜价
the amount charged for a service that is lower than usual because there is not so much demand for the service at that time
Cheap rate for overseas phone calls is from 8 p.m. to 8 a.m. 打国际长途的优惠时段是从晚上8点至早上8点。