Dear PakSKKU,
Aslam o Aliekum
I visited a place near gangan-gu office for an open market to find a double stroller for babies but it was closed. I will share about this open and sometimes called free market later as i could not observe it.
Fortunately, I found couple of shops which surprised me in term of price at which i bought those items. For example; a pair of socks for ladies or gents is 200 won only, so I bought 10 in 2000 won (For ladies pink color tag and for gents is blue one). Also DC batteries I found were 500 won for 4, which i bought earlier from a discount store at 2500. Most of the items attached at 200-1000 won and there are other items on the shop for which you might be interested. A bus route is attached for your information, a red stop is where you should take off the bus "gangan-gu office" or homeplus. Theses shops are near homeplus and can show picture of the shop and anyone could be able to tell you. Socks are displayed outside the shop and shop is at corner of the block where homeplus us. Socks are bought from one shop and rest of the items from another one. If need any help let me know.
I hope this will be helpful.
Best Regards