As it shown with how Jung Uk had 5 billion won on his account after investing two large ones, means that a large one is 1 billion won. So 500 large ones = 500 billion won.
The owners of Dramacool's sites and co. announced almost a month ago on Twitter that their sites would be closed due to the DMCA (they haven't closed them yet, but they stopped uploading). They didn't mention Myasian, but I think the sites scrap the content from their sites, so...
Gosh I really want them to be a pair...do you know if it's confirmed that they will be a couple?
Well, according to the character chart on the official site, unlike the obvious pairs that are linked with a heart shape in the middle, Do Jun's arrow to Mari says "Interest". So...maybe he will care for her as a little sister until she grows mentally... honestly, don't know how it will unfold.
So 500 large ones = 500 billion won.