Looks like I am pretty late to this party but if you're looking for serious bulk, ESfood actually has some really good PG and VG which is not cheaper than that Gmarket guy for small quantities but under 20,000 (including delivery) gets you 1kg of each (I forget my calculations but a bit over 900ml I think each)...
I found the link a while back on some Korean e-cig user's blog and ESFood even has some notes in their forums / Q&A sections that it is safe for vaping (and I myself have been using them for 2 years). They also have flavors (oil and non-oil based but I've given up on playing with them... I am satisfied with Lorann's from ebay).
PG:
[ES
VG:
[ES
It is a pain in the .... to sign up for a membership at ESfood but if you want the dirt-cheap price, it's totally worth it.
And in a pinch, you can get 50g of glycerine (say it's for your gf's hair if they get weird) from a pharmacy for 1000 won (a bit milky-looking but vapes fine).