The amount of financial security to be posted for the completion or required improvements shall be equal to 110% of the cost of completion, estimated as of 90 days following the scheduled completion date. The amount of the required financial security shall be based upon a written estimated cost of completion of required improvements submitted by the developer or applicant and prepared by a professional engineer licensed as such by the Commonwealth. Said engineer shall certify, in writing, that his estimated cost for the completion of the required improvements is a fair and reasonable estimate. The Borough Council, upon the recommendation of the Borough Engineer, may, for good cause shown, refuse to accept the developer's estimated cost. In cases where the Borough and the developer or applicant are unable to agree on an estimate, then the estimate shall be recalculated and recertified by another licensed professional engineer mutually accepted by the Borough and the developer or applicant. The estimate certified by the third-party engineer, being presumed fair and reasonable, shall be deemed the final estimate. In the event that the third-party engineer is chosen, the cost of his services shall be paid equally by the Borough and the developer or applicant.