If its convenient, the place with the best prices and most variety is Yongsan Electronics Market
The Yongsan Electronics Market is an enormous wholesale electronics market located near the Yongsan Train Station. The electronics market specializes in various consumer electronics including computers, computer parts, DVDs, CDs, and many other types of electronic goods. There are more than 3,000 stores situated in this area, with a number of large shopping malls such as Jeonja Land, Najin Sangga (Shopping Mall), Seonin Sangga, Wonhyo Sangga, Computer Domae Sangga (Wholesale Shopping Mall), and the Gwangwang Bus Terminal. Shoppers will find all their electronics needs at prices 15 to 30% cheaper than at retailers.
Jeonja Land (Electronic Land) in building 9 (9-dong) carries electronic parts on the first floor, broadcasting equipment and audio systems on the second floor, and computers and computer accessories on the third and fourth floors. The Wonhyo Sangga in buildings 4 and 5 (4- and 5-dong) provides lighting fixtures, along with electric and electronic parts. The Computer Wholesale Shopping Mall in buildings 6 and 7 (6- and 7-dong) carries computers, computer-related products and accessories, and also handles software development projects. The Seonin Sangga in buildings 21 and 22 (21- and 22-dong) deals in electric parts and electronic equipment on the first three floors, and computers and peripheral products on the fourth floors of both buildings. The Najin Sangga in buildings 10-20 offers lighting fixtures and home appliances in buildings 10-16, and computers, periphery products, and audio systems in buildings 17-20. At the Gwangwang Bus Terminal you will find computers, imported audio systems, electronic calculators, and a wide selection of video games and systems.