Hotels in Seoul is expensive, if you don't mind that no one to make up your room everyday and change you towels everyday, stay at apartment is a good choice.
I manage to get a this great apartment thur Airbnb, it is at a great location, airport bus stop and subway is just at the door step. Staying in this apartment for 6 days save me almost S$500 compare to staying hotel.
From the airport take bus 6011, cost 10,000won and it take about 1.5hours to reach the apartment.
It is much more expensive then taking the subway but will be more convenient as you don't have to carry you luggage up and down to transfer other Line train.
The apartment come with kitchen, which allow you to do simple cooking if you feel hungry late at night.
The toilet is clean and come with shampoo, shower gel. There is a washing machine in the toilet to let you do some washing.
This apartment come with a queen and a single bed + a sofa bed, can sleep up to 5 paxs.
This apartment is big and have a lot of space for our luggage which some of the hotel in Seoul don't have.
Only one down point is that the air-con is not working fine, however I travel during mid April which for Korean they don't on air-con during this period, with the window open it can cool the room up already
Insadong Main Street is just behind the apartment which have a lot of nice foods.