(a) In general 
There are authorized to be appropriated such sums as may be necessary to carry out this part.

(b) Availability of appropriations 
Notwithstanding any other provision of this subchapter, the provision of funds under this subchapter shall be subject to the availability of appropriations and the Secretary is not required to reduce funding for programs, projects, or activities serving a tribe in order to make funds available to another tribe or tribal organization under this subchapter.