I've done the New York Writers Workshop and I loved it. I also did the Writer's Voice, which shares a lot of the instructors with NY Writers Workshop. Your experience in a workshop will very much depend on the instructor, so more than anything, research him or her. I recommend trying to get into the advanced level classes because the caliber of the participants there can be very impressive. I found the money to be well spent because I don't think I would have ever finished writing the book without a structured setting where I had deadlines and also people shredding my work to bits (constructively, of course). I don't feel the need to do a workshop again, but for a first book the setting was invaluable. I really learned a lot. And as for the cost, think of it this way . . . if you were doing an MFA in creative writing, the tuition for similar classes would be well more than $20K per year. Of course, the workshops you mentioned don't give you the same pedigree as an MFA (or, you know, the degree), but you will learn a lot of similar skills.
Now, as for free . . . sadly, I don't know any good alternatives. However, a lot of people who do workshops tend to find their lifelong beta readers there. I still meet with a core group of writers that I first met through the workshop. We meet on a regular basis to talk about and critique our work, all free of charge.
Now, as for free . . . sadly, I don't know any good alternatives. However, a lot of people who do workshops tend to find their lifelong beta readers there. I still meet with a core group of writers that I first met through the workshop. We meet on a regular basis to talk about and critique our work, all free of charge.