The Vipassana silent courses put on by dhamma.org are entirely free, run by volunteers. The popular locations are fully booked months in advance, but if you have a very flexible schedule you can get on the waitlist and be accepted right before the course, that is how I did my first one.

I've done two 10-day courses from them. After my first one I described it to people as like being in prison, never having gone to prison, but with less freedom than prison. But I still went back for a second time :)