Hi,
I know where you can get intros to yoga but *cheap* intros are a bit harder to find.
The Bikram Yoga school at 618 Washington (maybe #620) offers 3 classes to be taken in a week for $20 if you've never been there before. I personally go there all the time and I love it. 10 class card is $150 (with discount if you are new) and 1 year is $1350. see website
www.bikramyogahudson.com
Another option is Yoga Shunya in Jersey City. They sell a 5 class card for $55. see www.yogashunya.com
In general yoga is not a cheap hobby but I can tell it will save you thousands in dr. and chiropractic bills if you practice regularly.