Expensive, you wont believe what Del Mar did this year. There were so many spa dealers wanting into that show, they made them bid on the booths in sealed bids. This did two things, vastly increasedc the price of booth spas, and elimnated MANY reputable dealers that couldn't aford more than 8 or 10K to be in the show. The high bid to get into the show came from calspas (factory sponsored) @ $150,000. The loest bid to get into the show, i forget who it was, was $65,000. If you buy a spa at the del mar fair, I'd guess you are getting majorly screwed.
Yes, as a rule, prices are higher at shows and fairs. It is very expensive to rent the space, pay all the people to set up and tear down, electricity (yup), and then to set up a dozen spas.