may be the same principle, years back was involved in having a stand at a engineering show. That got more and more expensive every year. The show organiser said they took the cost of running the show, hall hire, their staff present to then determine the cost to them of putting on the show.
They calculated the attending trade stand costs to cover the costs of putting on the show.
Then every ticket sold was profit, the risk being very few buy tickets to attend resulting in unhappy traders in attendances or lots of tickets sold very happy traders and a nice profit for the organisers.