I think you've hit the nail on the head there: a good negotiator is going to be expensive. I have a suspicion that it won't be worth the savings.
The phone operators at the other end would most likely be equally unskilled, with set concessions they can make to customers.
If your negotiator is just a script, then that isn't negotiating. The phone company won't be worried about losing the contract.
Think about it this way: if it's just a script, then why do you need a negotiator at all?