Section 25A. Unless the court shall otherwise determine, the prevailing party shall be allowed a sum not exceeding five hundred dollars for expenses actually incurred for plans, drawings, photographs and certified copies of public and court records, necessary and used at the trial. Except by order of the court, no such allowance shall be made unless an affidavit by the prevailing party or his attorney of record is filed with the clerk before final judgment, setting out fully such expenditures, and that said plans, drawings, photographs and copies were actually used at the trial.