No person shall be excused from attending and testifying in obedience to a subpoena issued hereunder on the ground of failure of tender or payment of a witness fee or mileage fee unless the witness makes demand for such payment as a condition precedent to the giving of testimony or the production of documents required by the subpoena, and unless such payment is not thereupon made. No insurer, agent, broker, solicitor or other person subject to the provisions of this chapter whose conduct, condition or practices are being investigated, and no officer, director or employee of any such person, shall be entitled to witness or mileage fees. In the event that witness or mileage fees are demanded and paid, the amount of same shall be determined as $10 for each day of attendance and 10¢ per mile for each mile necessarily traveled to the place of attendance, and the same for returning. The sum to which a witness is entitled shall be paid out of the treasury in any case in which the attendance is for the commissioner. In all other cases, it shall be paid by the person at whose instance the summons is issued.