Korean doughnuts or kkwabaegi can be found in most busy streets of Seoul, and this one (Jamidang) can be found near the streets of Bukchon.
It's all for very fair prices as the donut I show below was around ₩2,000 for three. A lady who had been standing near had proclaimed: "Every one of them is good! Every one of them!" when I had asked which she preferred. I sadly couldn't test her statement, but I believe her enough.