Only costs necessary and proper for completion of a project will be eligible under a grant or loan approved by the commission. The staff shall make a preliminary determination as to the allowance of costs. Such determination of allowance shall be final unless appealed by the sponsor to the commission. An appeal shall be filed in writing with the executive director who shall forward the same to the commission for its consideration. Unless specifically authorized by the commission or by this subchapter, no costs, except for engineering and property acquisition costs, incurred prior to the approval of a grant or loan agreement will be eligible for reimbursement.