Any such experts or consultants, while serving pursuant to such contracts, shall be entitled to receive compensation at rates fixed by the Secretary, but not exceeding the daily equivalent of the rate of pay for level 4 of the Senior Executive Service Schedule under
section 5382 of title 5, including travel time, and while so serving away from their homes or regular places of business, they may be allowed travel expenses, including per diem in lieu of subsistence, as authorized by
section 5703 of title 5 for persons in the Government service employed intermittently.