You can now fly over to Japan for very cheap, If I were in Korea I would look to make at least one big trip out here in the best season.
Route Map | Peach Aviation
This cheap no frills airline will fly from Busan and Seoul to Osaka and you can connect to fly up to Sapporo. If you book well in advance it can be super cheap.
From Sapporo an hour or two by bus gets you into some of the best powder in the world