(a) All contracts for new construction estimated to cost in excess of twenty-five thousand dollars ($25,000) shall be let to the lowest responsible bidder after competitive bidding.
(b) All contracts for alterations, maintenance, or repairs estimated to cost in excess of twenty-five thousand dollars ($25,000) shall be let to the lowest responsible bidder after competitive bidding.
(c) All contracts for materials and supplies not related to new construction, alterations, maintenance, or repairs estimated to cost in excess of twenty-five thousand dollars ($25,000) shall be let to the lowest responsible bidder after competitive bidding.
(d) A district may purchase in the open market without calling for bids, materials and supplies estimated to cost less than twenty-five thousand dollars ($25,000) for use in the work either under contract or by force account.