I've participated as a student, not an organizer, in guild workshops.
From what I can see, our guild has a set price per workshop - $25 for members and $40 for non-members if there are still spaces. The guild collects all of the registration fees and would retain fees above and beyond what they negotiated with the instructor or cover any deficit. At the end of the year, I think it balances out.
The instructor should provide a supply list (and it should be the correct supply list - one of the workshops I attended, it had been so long since she last taught that particular one, that she attached a supply list without proofing it first. There weren't critical items missing, but they would have been nice to have).
The instructor would collect the "kit fees" if there are required or optional kits, and I would expect there to be enough available for all participants.
A well organized and well run workshop is something that keeps guild members happy and returning. Our guild just announced two exciting instructors for next year, though not which of their workshops will be offered. I'll definitely be rejoining in January.
Cheers, K