Hi, I know this thread is from August; but we got off the Magic yesterday and wanted to provide some current information.
There was no charge to take a spin class. Olivia (trainer on board) put emphasis on the fact that you needed to sign up for the class; one gentleman did not, and she was trying to convey the message to him. Luckily, it was not a full class.
As for trying to create your own class, the cycles are all pushed together against the center window. There are signs on each side of the walls bookending the spin bikes stating that the cycles are to be used during class only. Also, the seats for the cycles are removed while not in use. Unless you want to do your own class in positions 2 and 3 the entire time, they would be of no use outside of an instructor-led class. I took photos in case anyone needed proof.