Based on previous Formation Arts,
Japanese retail ought to be about 780yen (US$7).
Import stores(play-asia, ningyoushi etc) will get them for about $10++ each
Diamond may as well. They released blister versions (original Japanese versions were blind boxed) for $14.99 ea.
Here's the link to the Kingdom Hearts set they offered:http://www.diamondcomics.com/pr/pr.asp?ai=30814&si=45