1. from Busan
You may use Gyeongju/Pohang Limousine Bus between Gimhae International Airport and Pohang Intercity Bus Terminal. It takes 1 hour and 50 minutes and the cost is KRW 11,000. The time table is as follows:
From Pohang Intercity Bus Terminal, a cab will cost about KRW 4,000 (~10 minutes) to POSCO International Center.
2. from Seoul
1 hour from Incheon International Airport to Seoul Station by AREX + 2.5 hours to Pohang Station by KTX.
A cab ride will cost about KRW 10,000 (< 30 minutes) from Pohang KTX Station to POSCO International Center.
3. via Pohang Airport
There are a couple of flights per day from Gimpo International Airport to Pohang Airport (see KoreanAir).
A cab will cost about KRW 15,000 (~ 40 minutes) from Pohang Airport to POSCO International Center.