We regularly send samples from the UK all around SE Asia. Each of our samples are 20kg.
We use Parcel2Go who still use the big boys as the couriers. Prices are very competitive (read cheap) and in 150+ times we have used them over the past couple of years only one problem and that was to Mongolia.
Just seen £54.00 for 8kg with 35x35x45cm with TNT into Thailand
Price change daily as supply and demand dictates
Worth a try?