Whenever I need a coffee quick fix, this is what I take - Nescafe. Six 180ml cans of sugar-ed milked coffee for KRW1,400. Good deal.
There's several brands in the market, like Lotte, Maeil, Maxwell House and even Starbucks. But I'll pass on Starbuck's bottled Frappucino at KRW2,600 per bottle. Some of the other brands are a little mild for me. This one is just nice.