Nothing, there's no monetary obligation at all, from registering until you leave. It will only cost you time and dedication, for 10 consecutive days.

AFAIK it's free. I know that the center in Delaware that I've looked to going to is free.

[edit] Yup, the article address this: ...these courses are 100% financed by voluntary gifts from previous students (who are explicitly asked not to donate anything unless it is from the pure wish of helping other people).