Contracts and agreements for furnishing the Municipality with labor and materials and for the purchase by the Municipality of supplies, materials, and equipment shall be made after competitive bidding pursuant to plans and specifications approved by Council, in the manner provided by this Charter and by ordinance, or, to the extent not so provided, in the manner provided by general law. Plans and specifications shall be prepared by, or under the supervision of the Board of Control. The Board of Control shall open bids and determine the lowest and/or best bidder. The Board of Control shall be entitled to enter into such contracts and agreements without competitive bidding in such amounts as may be authorized by general law.