Many good teachers have not been mentioned.
I've taken intensives with
Ted Matson - currently at the Huntington
Colin Lewis, - New England
Jim Doyle - Pennsylvania?
Todd Schlafer - Colorado based last I checked
Mat Reel - Pacific Northwest
Owen Reich - Midwest, I think Louisville
Suthin east coast and semi retired.
Peter Tea - California, not too far from Sacramento
All were at least good teachers, Ted was the best, well rounded whole spectrum of bonsai teacher. My first and 3 sessions a year for 4 years. Peter Tea was another favorite, Milwaukee society brought him in for 6 years, 3 times a year. For both we worked on our own trees. The situation Adair described, where you work on the teacher's trees only happens when you go to the teacher. In my case, the Milwaukee Bonsai Society brought the teachers to Milwaukee. We would sign up to share the teachers in small groups. For example, I was in a 5 person group that shared Peter Tea for a 10 hour day. The following day a 6 person group had him, then he had 2 days of single person class at that person's house. The club picked up airfares and the artist was hosted by one member for the 4 or 5 days the teacher was in town.
Many on the list donated a day to work with the local middle school bonsai club. You should see Colin Lewis with a pack of 9 to 12 year olds, he's an ideal grandfather type. Ted, Peter, Todd, Maru Stemberger, Jim Doyle all were great with the kids.
When sharing an artist, for example 5 students in 8 hours, each person gets 96 minutes with the teacher. Some one of the group serves as time keeper. We set up in the round so all can see and hear what is being said. Group discussion during lunch & breaks usually make it a long day for the artist. Hosting is at a member's house, or sometimes at the botanic garden that hosts the club.
When an artist is shared by a group, it brings the cost of studying with a top name artist down from the thousands to the low or middle hundreds. Most of the artists charge roughly the same daily rate, travel expenses are a big variable. Ryan Neil is an outlier, charging much more than the others.
It's been over 2 years since I was involved in booking an artist, so my cost information might be out of date.