There is also the Busan-jin market, in Busan. If I remember correctly, you get off at the stop before Busan-jin station on subway line 1 and when you exit you will see a 5 story 1 city block market with absolutely everything sewing inside it. On the streets surrounding this monolith are many sewing machine shops, which sell rebuilt second hand sewing machines. I looked at buying a 4thread over-locker for my sewing mad girlfriend and the guy only wanted 30,000won for it. It was in top condition too. If you're here for a short time it may be worth a Saturday to go check it out, instead of buying a new one at the going rate. Good luck.