Yeah - I would be interested in the cost. The website doesn't say.
I know many organisations need to charge volunteers, because it isn't easy nor free to take care of volunteers. And if a bit extra money gets to the project to keep it running - GREAT.
But, along the lines of Wanding_Mans suggestion - Mae Tao Clinic is a free volunteer option. Again on the Thai Burmese border. It is mainly suitable to medical volunteers, but I reckon it well may be one of the most amazing experiences of your life. Mainly for medical volunteers with a decent period of time to offer. Look it up if you are interested.
http://www.maetaoclinic.org/(By the way, I'm just going through the NEED website, and Wandering_Man's post from there. Very interesting)