The United States Commissioner is authorized to construct, equip, and operate and maintain all access roads, highways, railways, power lines, buildings, and facilities necessary in connection with any such project, and in his discretion to provide housing, subsistence, and medical and recreational facilities for the officers, agents, and employees of the United States, and/or for the contractors and their employees engaged in the construction, operation, and maintenance of any such project, and to make equitable charges therefor, or deductions from the salaries and wages due employees, or from progress payments due contractors, upon such terms and conditions as he may determine to be to the best interest of the United States, the sums of money so charged and collected or deducted to be credited to the appropriation for the project current at the time the obligations are incurred.