For carrying out the provisions of section 23 of the Federal Highway Act approved November 9, 1921 (23 U. S. C. 23), and for the construction, reconstruction, and maintenance of roads and trails on experimental areas under Forest Service administration, including not to exceed $59,500 for personal services in the District of Columbia, $2,537,168 for forest development roads and trails, representing the balance of the amount authorized to be appropriated therefor for the fiscal year 1943 by the Act of September 5, 1940 (54 Stat. 867), together with $1,241,555 from the unobligated balances of previous appropriations for forest highways which is hereby reappropriated for forest development roads and trails; in all, $3,778,723, to be immediately available and to remain available until expended: Provided, That this appropriation shall be available for the rental, purchase, or construction of buildings necessary for the storage and repair of equipment and supplies used for road and trail construction and maintenance, but the total cost of any such building purchased or constructed under this authorization shall not exceed $7,500.