Are there any stores here in Korea similar to the American stores like Dollar Tree, 99 Cent, or Family Dollar? Basically a store where everything is really cheap but still a decent quality.

That concept hadn't yet caught on when I was last there. I doubt it has now. Many bargains can still be found at the various Korean open markets, if you have a Korean friend with you who knows how to dicker over price.

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I found a little dollar store that is near Osan AFB. When you leave the walk through gate make a right and it's on the road that turns left at the Citi bank. It's the same road that 1-1 makes it last stop on. Once you make the left, it's not far on the right side. If you walk to the bus stop you walked too far. I noticed it when we went to the Thai restaurant that is advertised on this site.

Yep, they have them! Smaller, generally than a US version. There is a 2000won store in the Express bus terminal in South Seoul. (South of the river is usually higher prices.) A 1000 won (dollar) store is on an upper floor of the Yongsan Electronic Center in the big building with the appliances and movie on the top floor. There is one in the subway station near Myung Dong station. Of course they are not known as "Dollar" stores. Bargain stores maybe.

there is also one on the corner of namyong station

I think I am going to check them out, I had no idea they were here.

I LOVE that store!! I am literally in there like once a week. They always have new stuff, and the ladies are nice