CAS ULTRASOUND OR NORMAL ULTRASOUND? WHICH IS LESS EXPENSIVE Pero okay naman result?

Hello po, first time mommy po ako. Bale ready na po ako for ultrasound , 22 weeks na po kaso . Then sabi po ng OB ko na pede ako magpa CAS para mas sure or Normal Ultra, suggestion lang po, mas okay napo ba kahit normal nalang? SINCE LESS expensive.. or mas okay CAS? Please comment po.