Flying into Tivat Airport is typically the best way to visit Kotor Old Town Walls, since it is the closest airport to the area.
If you are looking to fly to Montenegro for less, look to airlines like Ryanair, Lauda, and Wizz Air, with prices starting at £17, £21, and £28 respectively.
Montenegro has suspended all commercial flights and restricted the entry of travelers who are not nationals or residents of Montenegro; however as of June 1 it has opened its borders to travelers from a select group of countries meeting certain epidemiological criteria: Slovenia, Iceland, Croatia, Slovakia, Switzerland, Albania, Austria, Norway, Monaco, Kosovo, Denmark, Lithuania, Latvia, Azerbaijan, Luxembourg, Bosnia and Herzegovina, Bulgaria, Israel, North Macedonia, Germany, Poland, Czech Republic, Hungary, Albania and Greece, Ireland, Finland and Estonia. The list is expected to be updated every 2 weeks. All travelers entering Montenegro from abroad should expect to be subject to a self-isolation period of at least 14 days. If you are planning to travel to Montenegro at this time, it is recommended that you stay up to date on current restrictions and follow proper safety measures while in public.