employ experts and consultants or organizations thereof as authorized by
section 3109 of title 5, except that contracts for such employment may be renewed annually; compensate individuals so employed at rates not in excess of the rate specified at the time of service for grade GS–18 under
section 5332 of title 5, including traveltime, and allow them while away from their homes or regular places of business, 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, while so employed.