Is clinical breast exam needed before mammogram? Considering cost, I think should be done.

Not required. It is preferential to do a clinical breast exam yearly in women over age 40, however, a mammogram can "see" and detect growths that are sometimes not clincially palpable. The best advice here is to do breast self exam monthly after the menstrual period starts to eliminate the breast swelling that occurs before the period.
Physical exam. It is a complementary examination. Physical exam can pick up a small percentage of cancers not seen on mammo. However, it is not required in order to have a mammogram.