I have been going to a retreat sponsored by one of my two guilds every year for the last 10. It is a lot of fun. In my experience unless it is set up by a professional quilter looking to make a profit, retreats are sponsored by local guilds. This past fall it cost me $165.00 for 4 days with 9 meals included. We had to take our own linens. In both of my guilds space is limited to a certain number of people which is usually only 20 or 25% of the membership. The only time they open it to outsiders is when they can't make their minimum requirements for the facility. It seems to work best in my opionion when there are no more than 24 or so people and each person is able to have thier own table for setting up. That is the way the retreat I go to usually works. I have not been on retreat with the other guild and at this point I am not interested. They take as many as 50 people and have every other hour of your stay filled with some activity. I think that is too many people and too much organization. I don't consider it a retreat if I am obligated to do all of the projects everyone else is doing. I prefer to take my own work. THe retreat I do attend usually has one project that is offered to the members but it is not obligitory.
If you go on a retreat be prepared to drag the kitchen sink. Some of our members actually bring their own chair and or table as well as their machines, irons, ironing boards, cutting mats etc. etc. etc. One lady has a van that is stocked almost like a quilt shop with fabric, batting, thread etc.
Some guilds have a speaker or teacher come in for the group. That can get very expensive. I have a friend that took a quilt cruise through parts of Europe. It featured mostly lectures on techiniques and handwork. At least they didn't have to drag a sewing machine. Other cruises involve a sewing machine etc. The best ones provide everything you might need either for rent or sale. They can get really expensive.