In Australia you can place a different number in the phone with your big ad, and they will track the calls to see if the ad is working or not.
Cost ?? would not have the foggiest idea as I dont advertise in any form
All advice is given with-out seeing the job, and hence all advice MUST be taken as advice with limited knowledge on the exact situation. NO responsibility can or will be taken. And yes, I am a licensed Plumber and Drainer with my own business in Brisbane Australia