Flying to South Korea - How much usually?

HI, I might be flying to South Korea and was wondering how much flights usually are from Tokyo - Seoul? What`s the cheapest you`ve paid?

and if you know any good travel websites/travel agents, that would be appreciated! Thanks

forgot to mention I`m pretty flexible with dates from March - June. From Narita - Seoul

I took a high speed boat from Fukuoka. Around 200 bucks. I can't remember. I would check with JTB travel agency in Japan.

This website gives you some ideas of airfares, which can be cheaper than a one way journey from Tokyo to Fukuoka by train. But be aware that there are a few hidden fees such as airport taxes and fuel surcharges, not included in the advertised rates:
http://www.no1-travel.com/

By no means am I saying use a boat from Fukuoka because you're far away, you can probably get a good ticket for under 500. It's about an hour flight....It was cool to take the boat there though!