A municipality is prohibited from negotiating a contract except a contract:

(1) Involving the expenditure of less than $20,000.00;

(2) With a state agency or political subdivision as authorized by Code Sections 32-4-111 and 32-4-112;

(3) With a railroad or railway company or a publicly or privately owned utility as authorized by Article 6 of Chapter 6 of this title;

(4) For engineering or other kinds of professional or specialized services;

(5) For emergency maintenance requiring immediate repairs to a public road, including but not limited to bridge repairs, snow and ice removal, and repairs due to flood conditions; or

(6) Otherwise expressly authorized by law.