According to a Sports Illustrated report (via Sanspo), the A's winning bid about US$17M. The Twins are said to have made the second high bid and the Minnesota Star Trinbune's Seth Stohs feels their bid may have been somewhere in between US$10-15M (via Nikkan Sports).
Some comments from Hisashi Iwakuma (found in the above Sanspo link):
I'm happy. I was a little surprised because it was a team that the papers didn't mention very much. Since I don't really know much about the team, I'd like to do a little research on them.
[This means] I get to pitch against the world-famous Ichiro.
If it's a toss-up between starting and relieving, I'd rather start. The living conditions / environment, the position, these are thing I will speak to my agent about and decide on.