The Secretary of the Interior is authorized to acquire on behalf of the United States by purchase, at prices deemed by him to be reasonable, the lands needed to complete the Great Smoky Mountains National Park in the State of Tennessee, in accordance with the provisions of sections
403 and
403a to
403c of this title; and the Secretary of the Interior is further authorized, when in his opinion unreasonable prices are asked for any of such lands, to acquire the same by condemnation under the provisions of section
3113 of title
40.