Is there a market in Seoul were i can buy traditional Korean items?

and what type of thing would be able to buy

and how much does a korean sword cost

insadong and itaewon. you can buy those traditional bamboo square pillows. I cant rmr what they are called though.
as for how much a korean sword costs...i'm not too sure.

Almost any of the main shopping districts in Seoul will sell traditional Korean items. If there are basement stores, those are the most likely to have the best stuff. You can try Gangnam, Insadong, and Myong-dong for the best shopping. But if you want a good authentic Korean sword, try Insadong. There is an alley way between at the bank at the main 4 way intersection there, where you go down to a basement shop and they have authentic weapons from all over from all time periods.

You'd have to go to touristy places such as Itaewon. It can a little pricy because the shops are aimed at tourists. However there are some quality items.

Remember ALWAYS haggle.

Insadong/Jongro 3ga Area
Orange Line: Anguk station or Jongo 3ga station
It's the historic/Arts district. Insadong street is nothing but a looong row of traditional Korean pottery, paintings, and souvenirs galore. Next to Insadong is Jongro jewelry district (rows of gold and silver stores) and the Namwon Arcade (four levels of musical instruments). Because there are so many of the same stores in one district, I've found the best prices there (better than Itaewon) especially on ceramics and souvenirs.

You can also try the flea market inside Dongdaemun Stadium. I've often seen random sundries such as a sword being sold there. But if you're looking for an authentic antique, Insadong is your best bet.

It has been almost 10 years since I was in Korea, but I loved Insadong (the antique market). I bought a 19th century Chinese dadao (war sword) there for a decent price, but at the time the dollar to won ratio was through the roof (about 1600won to the dollar). It is also the art market area and I assure you, you will not be disappointed visiting it.

I believe Jongno 3-ga is the closest subway station.