When a board of law library trustees in any county determines to erect a library building to house the law library, it may borrow money for that purpose and repay the loan from its future income. The board may borrow the money from any person, or private or public agency, or corporation, in an amount not exceeding half of the funds of the board allocated to the construction of the building, upon such terms as may be agreed upon by the board and the lender and approved by resolution of the board of supervisors of the county.