Just thought I'd share my experience of getting to Incheon Airport - and maybe help you save some money.
Unfortunately, because I got offloaded, I went to the airport twice. The first trip was in a taxi and it cost me approximately 100,000 in local currency. The second time I actually took what's called the Korean airlines chauffeur bus. It cost me 15,000 which is a fraction of the price and it took the same time to get there. The seats are incredibly luxurious and much more comfortable than sitting in a taxi. It gives a great view of the city, it arrived on time, it departed on time and the seats even reclined quite some way so you could even get a bit of a snooze.