Grocery prices in Korea

I just moved to Seoul from Singapore. My Korean wife keeps telling me that grocery is cheaper in Korean. I beg to differ. I just paid 10k won for 1kg of sweet potato and 18k won for a loaf of sourdough. My wife keeps finding excuses for why certain items are more expensive here, usually along the lines of "oh that's imported" or "that's domestically produce...and there is no foreign competition" or "you're paying more for better quality" or "korean mountain vegetables are much cheaper in Korea. I keep pointing out that a lot of items that we eat are more expensive here than in Singapore (FairPrice) and she keeps arguing with me and telling me they are not. Drives me fucking insane. I mean I have fucking eyes!