Food in Korea is really quite easy to come by and really tasty pretty much wherever you go but the best restaurant that I went to was a little restaurant in an alleyway. It was the best KBBQ that I have ever been to, and probably will ever go to unless I make a trip back, and was pretty much cheap as chips. We paid about $12 each to be completely stuffed and a bottle of soju and 2 cans of coke. The reason for the drinks was that I'm not a big drinker but Simon and Martina from eatyourkimchi recommended to try soju and coke together and I have to say it's pretty good. 

If you like your fruit, I would definitely gear yourself up to be missing them your entire trip unless you are willing to pay up to $5 for ONE apple or head to the countryside. The cheapest fruit that we came by was $5 for a bag of apples and $3 for a bag of mandarins, with each bag containing 5-6 pieces of fruit, that was sold in a small stall owned by a really sweet old couple. It is rare to come by fruit that cheap but man their fruit is on extreme steroids or something as everything was enormous and perfect looking except for the ones that we bought. 

Drinks are also really cheap both alcoholic and non-alcoholic. If you are into cocktails, then you are looking at about an average of $4 a drink with Korean alcoholic drinks such as soju being really cheap at about $3-6 a bottle. With those cheap prices, you are bound to see some drunk men roaming the streets especially if you out past 10/11pm.