We stayed in an Airbnb while in Seoul. The Airbnb was near Hongik University which was a perfect location as it was on the airport subway line and near lots of good bars and restaurants. For €94 we got a private twin room with a shared bathroom, free washing facilities, filtered water and breakfast included. The Airbnb host provided us with eggs and bread each morning to make our own breakfast.
Seoul has an excellent subway system. On average the cost of a one way subway ticket was 1350 Korean Won which is about €1.02 per ride. Very affordable.
We saved a lot of money by eating the breakfast provided by our Airbnb host and by not having to purchase bottled water. We did however spend money when it came to dinner. As we were only in Seoul for a short period of time we had a list of meals we wanted to try. From Korean BBQ, Bimbimap and Chimac (Korean friend chicken and beer). Dinner each came in around on average €20 for two plus extra for beers. The average price for a bottle of beer was around 5000 Won €3.80.
We spent 1000 Won in a pharmacy on a packet of tissues, and thats as it for any general expenses.
Sightseeing / Activities:
Seoul is a great city for free things to do. Most of our activities were free such as climbing to the top of Seoul Tower hill, taking a walk around Bukchon Hanok Village and hiking to the top of the highest peek in the Bukhansan National Park. We only paid to do two activities and those were a food tour booked through Airbnb (44 euro per person) and our entrance tickets into Gyeongbokgung Palace (3000 won per person).