The board of regents shall enter into such contracts with one or more contractors for the erection and construction of university buildings or improvements thereto as in their judgment shall be deemed for the best interest of the university; such contract or contracts shall be let after public notice and under such regulations as shall be established by said board or as otherwise provided by law to the person or persons able to perform the same on the most advantageous terms: PROVIDED, That in all cases said board shall require from contractors a good and sufficient bond for the faithful performance of the work, and the full protection of the state against mechanics' and other liens: AND PROVIDED FURTHER, That the board shall not have the power to enter into any contract for the erection of any buildings or improvements which shall bind said board to pay out any sum of money in excess of the amount provided for said purpose.