I just looked at healthkoreaus.com and it seems to have some really good prices I have seen in a while. I have been having a Korean friend order protein for me on that xspeed.co.kr (or something like that) and it was maybe 10,000 won more there.
When i ordered from Bodybuilding.com in the past, they would always decline my credit cards, and when i questioned them about it, they said it was an issue with credit card fraud out here in korea. I had to set it up where i just do bank transfers to them.
If Healthkoreaus.com has a $10 flat shipping fee as a previous poster had written, I think its the best deal around..