You can check the various rates for Thailand Post here:
http://www.thailandpost.com/rate.php
They have an EMS World one-price box to the U.S.A. for 1,400 baht. They can help you pack the items.
You can also pack a box, maybe store it somewhere, even at the airport, and then check it in with UA. I always bring a big box from the U.S. to Thailand via UA.