No commissioner shall receive any compensation, whether in form of salary, per diem allowances or otherwise, for or in connection with his services as a commissioner, except that the Housing Authority in any municipality having over 500,000 inhabitants may establish by resolution a reasonable salary or per diem allowance for the services of the commissioner who serves as chairman, and except that in an Authority created by a municipality or a county having over 25,000 inhabitants the corporate authorities of the municipality or county may establish a reasonable per diem allowance for the services of commissioners, to be paid by the municipality or county from funds budgeted by the corporate or county authorities for that purpose. Each commissioner shall, however, be entitled to reimbursement out of funds available therefor, for any necessary expenditures in connection with the performance of his general duties or in connection with the construction or operation of any project. The Authority may allocate such expenses among its projects in a manner as it may consider proper. An Authority created by a municipality or county having over 25,000 inhabitants may also provide for the reimbursement, from funds of the Authority, of any travel expenses incurred by the commissioners for travel in connection with their duties.