We do a summer festival every year in July.  We have all of our insurance with All State Insurance.  When I need booth insurance, I call them and they set up the insurance for us, and then I send them a check for whatever the premium is, and that always depends on our location.  If we are at an indoor parking structure, we pay less for our liability insurance.  I guess that I can understand this,because one year  when we were in a downtown area of a small suburb, a tornado came out of no where and blew away most of our products and everyone else’s.  I felt so blessed to survive that event, but it would have been even worse if we did not have the insurance.  Try calling your current insurance company for a reference to someone who offers this kind of liability insurance.  You can ask other vendors who they use, or ask the person who is in charge of the event, if they recommend someone.  California has something called the California Fair Services Authority that sells about $100,000 worth of liability insurance for $84.  Your state may offer something similar.  Most states have State Fairs and that is probably how the practice got started.  Check it out, in your area.