Thanks for your response Mike. I only started looking yesterday, so I will spend more time analyzing availability and price change... but from your message, it appears I should just go ahead and book the optimal flight now, and if my situation changes, I can change and lose Krw10,000.
For the China flight, I was referring to flights departing CJU going to China perated by Chinese airlines. I know China domestic flights have very bad rep for postponement and cancellations, and was wondering the same for these once-a-day flights from CJU to various second-tier cities in China (SHE and XMN).