This is a site with ferrys to and from Japan:
Randy's 'Favorite Getaways in Rural Japan' -- INTERNATIONAL FERRIES
here is the link to the (fast) Ferry from Hakata to Pusan
Beetle English
One way fare is 13 000 円 and it takes 3 hours. (round trip 20 000 - 24 000)
There is also an overnight ferry from Hakata to Pusan
http://www.kampuferry.co.jp/ (japanese only) fare is 9 000 円
There is also a link from Shimonoseki to Pusan, for the overnight ferry ist 8 500 円
http://www.kampuferry.co.jp/ (japanese ONLY)
So it seams the fast ferry is a pretty good deal and has got an English homepage. But i´d rather take the overnight ferry for 9000 or the overnight first class for 10 000 - 12 000), i think its gonna be a special experience
Firebird