The following provisions shall apply with respect to the procurement of non-public works:
(a) A centralized purchasing system shall be established for the purchase, lease or other acquisition of all property, supplies, materials or equipment required by all City departments, offices and agencies.
(b) The City Manager shall recommend and the City Council shall consider and adopt, by ordinance, rules and regulations governing the purchase, lease or other acquisition of all such property, supplies, materials and equipment.
(c) The ordinance described in subsection (b), above, shall include provisions for competitive bidding. It shall also include such other provisions as may be necessary or appropriate to implement a procurement process that is consistent with best practices. The ordinance may also provide for one or more exceptions to the competitive bidding procedures, provided that any such exception is implemented as part of a City-wide policy or program that has been approved and determined to be in the best overall interests of the City by at least four affirmative votes of the City Council.