We were just there. Food is very reasonable, especially if you go to the “local” restaurants. You can get a pretty decent meal from 7,000 - 9,000 won (roughly $7-$9). Even if it is a total hole in the wall, it is likely to serve good food. I think there is so much competition in Korea that unless you serve good food, you will quickly go out of business. Don’t worry, all the menus are in English as well as Korean, and usually have pictures of the food as well.
One thing Koreans don’t eat is western-style breakfasts, so if you like that it can be hard unless you go to somewhere like McDonalds (which is Koreanized to an extent). An option is to go to one of the many upscale coffee places and get a coffee and a piece of fancy cake. (Something they are always doing in the K-Dramas.) That can cost you the equivalent of $10 but it is a nice experience. Quality of the coffee is much better than you would get at Starbucks, although it will not necessarily be as big.
The breakfast problem you mention is true throughout Asia, unfortunately for American travelers. Hotel buffets are usually the best solution - there isn't much on the street.