Gyeongju's major heritage areas, temples and outlying attractions are spread across the city, so a static list of bus numbers is a poor substitute for checking the route you actually need on the day. Gyeongju City's official transportation information center provides real-time bus information, route timetables, fare information and route search.
The official bus fare page currently lists the adult city-bus fare as KRW 1,500, with a KRW 50 discount when paying by card. It also says a transfer can be free within 30 minutes after tapping out, with one transfer, and that transferring to the same route is not eligible. Recheck the current fare page before travel because local rules can change.
If you arrive by rail or long-distance bus and are unsure which local route to take, Gyeongju's official tourism site lists tourist-information offices at Gyeongju Station and the terminal area, and states that foreign-language interpretation is available through its tourist-information network. The site also links to the national 1330 tourism interpretation line.
Do not assume that one city bus serves every famous site. Build the day one leg at a time: arrival hub to the first site, then the next site, then the return trip. For outer destinations, confirm the return bus before you leave the city center, especially late in the day.
Practical next step: open the official Gyeongju ITS/BIS on the travel day, search the exact stop and route for each leg, and keep the Korean name of your destination ready to show at a tourist-information desk or to a driver.