There are lots of opportunities to buy good and inexpensive good in Seoul's traditional markes. Among them is the "Dongdaemun Market" near Dongdaemun is the most famous of its kind in Korea. Here you can buy the latest fashions and prices are much cheaper than department stores. The area is so famous that it would be hard to find a young person who has never been there.
The Dongdaemun Market has established itself as the center of the Shopping mall beginning in the late 1990s, when shopping malls like Doota and Migliore opened up for busines. There are some 30,000 shops and stalls selling clothes, accessories and the various sundries. Moreove, and an estimated 2.5 million foreign tourists and merchants are said to visit every year. The government designated it a "special touris zone" in 2002.
Everything from designing, production, and sales takes place at Dongdaemun Market. It supplies the clothing shops for the whole country while also selling retail to incividual consumers. Both wholesale and retail sales take place 24 hours a day, so you can purchase clothes even in the wee hours of the morning, and even at night the area is filled with the large crowds.
There is even a "purchasing information center" exclusively for foreigners to help foreign industry buyers find the items they need. It can also helpt foreigners fill out the documentation necessary for shipping and other parts of large export transactions. It would be worth your time to go there if you stay in Seoul.