I don't know how they can get more vendors to show up. I was going to say, make the spaces REALLY cheap, but I looked up the cost and the spots are only $30. That's already pretty cheap. Maybe additional spaces could be $20? So, $50 for 2, $70 for 3. It might help.

I used to run an antique toy collector show with a buddy of mine. Part of our strategy was to have the cheapest vendor tables... And we did, and it worked! We always had plenty of vendors and plenty of patrons in a time when toy shows and vendors were really droppng off.