ameet0121,
There is no cost involved with rx/tx using ADS B as it is VHF. The refresh rate I mentioned earlier is for radar, ADS B may in fact recieve many more updates per second. I am sure 1 of the guys presently using it can give the exact figure. The cost with ADS C comes from using the satellites for the RX/TX and charged to the airlines by the provider, either ARINC or SITA. ADS B is not used over the ocean unless in range of a ground station, it is purely a VHF system. ADS B is used in Australia in areas that were previously non radar to significantly improve the service to the airlines. It is cheaper to install and maintain than a standard radar system as it requires no moving parts and therefore brilliant for areas that are remote. The Mode S you ask about is a radar function using the transponder to deliver information about the aircraft, heading speed etc. So is used in areas with radar coverage. I hope that answers your questions. Good luck with your new system, ADS and CPDLC are amazing once you come to terms with how useful they can be.