I am in India and I want to unlock Apple iPhone 3G and cheaper??

how and at what price i can get this

Unfortunately, there is no cheap way to do it, it will cost much to buy an unlocked iPhone, since you can buy a Vodafone or Airtel. They are just too popular and everyone wants one, you can end up paying more for an unlocked phone. See link below for more information.

Custom iPhone 3GS 32GB For Sale – Jailbroken & Unlocked