“Incremental costs”, as used in this article, mean any costs necessary for the establishment of a system required by this article and recommended for reimbursement by the advisory committee established by Section 53115.1 other than costs for (1) a basic system, (2) a basic system with telephone central office identification, or (3) a system employing automatic call routing, which are reasonable, necessary and unique for the planning and efficient implementation of a local agency’s 911 system.