When will you go? I will go to business trip on Apr, will stay behind for 3 nights by myself, I planned to go shopping too.
I booked K-Guesthouse Dongdaemun Premium, it costs less than $1000 for 3 nights. The location is very good as I checked the comments on booking.com.
The room is very small, but I think it is no problem as I will not stay in the hotel room except sleeping.