To be honest I do not know of a way to ship these cheaper than the flat rate boxes at the post office. The weight of the boxes are high due to the amount of books. I always try to help someone out. Let us make sure you win them then we can figure out shipping. Maybe you can just choose and pay for a particular book? I will try to think of other options!
Media mail - thats the way to go. You can probably ship them all much cheaper. Just use a plain box instead of flat rate box. post office will be glad to weigh them for you.