(a) General rule.--Except as provided in section 11901.4(b) (relating to contracts or purchases not requiring advertising or bidding), all contracts or purchases in excess of the base amount of $18,500, subject to adjustment under section 11903.1 (relating to adjustments to base amount based on Consumer Price Index for All Urban Consumers), shall be subject to advertising and competitive bidding as provided in this chapter.

(b) Contract.--All services and personal property required by any city municipal department, where the amount exceeds the base amount of $18,500, subject to adjustment under section 11903.1, shall be furnished and performed under written contract. The contract shall be awarded and given to the lowest responsible bidder after advertising two times, each publication on a different day, in not more than two newspapers of general circulation, in accordance with the provisions of section 10109 (relating to publication of notices). The bids shall not be opened until at least 10 days have elapsed after the first advertisement is published. A copy of the advertisement for contracts or purchases shall be posted in the city office designated by council.