Korail pass is having a price adjustment in July. For details like price and different passes, please check out Korail website.
My feeling on using Railpass in Korea-
After the price adjustment, I think it is not really a good value deal. I have used it before, and it was cheaper then. I just did some calculations last night for my upcoming trip and I found it is not much cheaper and the downside is that you cannot reserve the tix before you arrive in Korea, it is quite possible you cannot get the tix u want if u use it, and it is not that cheap