In any municipality having a population of 500,000 inhabitants or more, the president of the commission shall receive a salary of $7,500 a year, each of the other members of the commission shall receive a salary of $5,000 a year, and the chief examiner of the commission shall receive a salary to be fixed by the corporate authorities of such municipality. Any person not at the time in the official service of the municipality, serving as a member of the board of examiners or of a trial board, shall receive compensation for every day actually and necessarily spent in the discharge of his duty as an examiner or a member of the trial board at the rate of not exceeding $7 per day, and the commission may, in such municipality, also incur expenses not exceeding the amount appropriated therefor by the corporate authorities of the municipality wherein the commission exists. In municipalities having a population of less than 500,000 inhabitants, such commissioners and the chief examiner shall receive an annual salary, to be fixed by the corporate authorities of such municipalities. In any municipality having a population of less than 500,000 inhabitants, any person not at the time in the official service of the municipality, serving as a member of the board of examiners or of a trial board, shall receive compensation for every day actually and necessarily spent in the discharge of his duty as an examiner or member of the trial board at the rate per day to be fixed by the corporate authorities of such municipality, and the commission may, in such municipality also incur expenses not exceeding the amount appropriated therefor by the corporate authorities wherein the commission exists.