If money is an issue there is a Hostel which provides free pickup and will drop you off for your next flight.You can find its email if you check out Seoul Hostels I stayed with them about 5 months ago it was in a modern high rise which is quite nice I stayed with them again passing on return had room to myself both times (4 beds in room) but also had private rooms available located in area with several bars and resteraunts I think it was 15-20 usd