We went to Kaist Opticians.
First bought a pair of prescription glasses. The frames cost W20,000. The lenses? If you have a weak prescription the lenses cost W20,000~W40,000. Because I am basically blind my specially compressed and coated lenses cost W160,000, which is still several hundred dollars less than I would have to pay at home. The sunglasses are Ray Bans. W120,000 which is pretty standard.
They staff were pretty eager to help, and one older man even professed his love for Emilie (apparently she looks like a young Brooke Shields)
How to get there:
Take Subway line 4 (light blue) to Myeongdong station. Exit 5
Walk into the shopping area about 50m until the first intersection and turn left. Then walk another 50m or so. Kaist Opticians will be on the corner on the left.
Hint: Korean made frames are the cheap ones. I'll update again if they prove to be poor quality, but thus far seem to be holding up!