Unlike Scientology, Vipassana courses are free. They provide food, shelter, and an incredible experience on the donations of others. If you want to give a donation after you've finished the course (and only after you've finished the complete course, they won't accept donations otherwise), then you are welcomed to.
I have never done a Vipassana retreat, but I've played around with that style of meditation with good results. To me this is one of the most admirable aspects of it - so many of these so called "spiritual" (a misguided umbrella term) retreats/courses functions more as a way for the founder to get rich than to do something good. See the founder of Bikram yoga.
