Check with you local Janome dealer.
I have two Janomes, one is low shank the other is high shank. Which do you have? One has a acrylic extension table/tray, the other does not. Janome does not make acrylic extension table/trays for all their machine.
If this is a FMQ class, IMHO, for the LQS to say that you "need a Machine with Tray" is requesting a lot, not everyone has "trays" for their machine. Check to see if it is 'REQUIRED'. I took 2 FMQ classes (each at different shops) and neither asked for the tables/trays.
have fun!