If you are planning to visit Korea for a week then your approximate expenses (for people on a shoestring budget) for a city like Seoul or Busan would be as follows:

1. Accommodation (including breakfast & internet):
In a dorm could be around 22,000 – 25,000 won.
In a motel/officetel / Gosowon could be around 40,000 – 50,000 won.

2. Food:
Korean Meal: Per meal could cost around 5000 – 7000 won (no beef, only pork)
Western Meal: Burger – 4000 – 5000 won, Pizza  - 7000 – 20,000 won, Steak (oops we are on a shoestring budget so no steak, no pasta )
Indian Meal: Lunch Thali – 6000 – 7000 won, Dinner Set – 15000 – 25000 won

3. Drink:
Beer (Maekju) – 2000 –  5000 won per bottle (depending upon the restaurant). Works out much much cheaper if you buy it from a  convenience store / supermarket.
Soju (Korean Drink) – 1000 to 3000 won per bottle

4. Travelling (approx):
Subway – 1000 won per ride (minimum fare)
Bus  - 1000 won per ride (minimum fare)
Taxi / Cab – 2700 won (minimum fare)
Intercity Travel – could vary – but be ready to pay anywhere between 20,000 won to 30,000 won.

5. Other expenses:
Rental phone: If you have friends in Korea or are planning to meet a few people then it is a must. Rental phones are available at the airport on a refundable security deposit.
Travelling from Incheon Airport to your destination: If it is in Seoul then you need to pay anywhere around 20,000 – 25,000 won to use the city limousine bus. For Busan it could be around 40,000 won.
Travelling Card (T Money) – T Money cards are available at any convenience store for 3000 won and it is highly convenient if you need to travel in Seoul. It is acceptable in Subway, Buses as well as select Taxi. You need to charge it as per your usage. For a weeks travel it is safe to charge it for 30,000 – 35,000 won.
Entry Charges: Visiting certain museum, palace or public place will have entry charges ranging from 1000 – 4000 won.

So the minimum expenses in a city like Seoul or Busan for a week could work out to be (450,000 won / $450 / Rs. 20,000) excluding air fare…